Capacitor and method for producing the same, and circuit board with a built-in capacitor and method for producing the same

ABSTRACT

A miniature solid electrolytic capacitor is provided, which is suitable for being disposed within an electrically insulating layer, and is connected to other component using an electrically conductive adhesive with a connection resistance at an anode low and with connection reliability improved. Specifically, the electrolytic capacitor includes a valve metal element for an anode  10  having a capacitor forming part  10 A and an electrode lead part  10 B, a dielectric oxide film  11  formed on the valve element, a solid electrolyte layer  12  formed on the dielectric oxide film  11  and a charge collecting element for a cathode  13  formed on the solid electrolyte layer  12 , wherein at least one through hole  15  is formed in the electrode lead part  10 B so as to expose a core  10 C of the valve metal element, and an exposed portion  10 D of the core is used for connecting portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims a priority under 35 U.S.C. §119 toJapanese Patent Application No. 2002-379231 filed on Dec. 27, 2002,entitled “Capacitor and method for producing the same, and circuit boardwith a built-in capacitor and method for producing the same.” Thecontents of that application are incorporated herein by the referencethereto in their entirety.

FIELD OF THE INVENTION

[0002] The present invention relates to an electrolytic capacitor whichcan be built in a substrate, a circuit board with the capacitorbuilt-in, and a functional module with the capacitor built-in.

BACKGROUND OF THE INVENTION

[0003] Recently, as an electric and electronic device become moreminiature and more high-density, there are employed many techniqueswherein a circuit board having a plurality of components is modularizedas a package for each functional block, and the necessary modules arecombined so as to obtain a predetermined electrical circuit, as asubstitute for a prior technique wherein individual components aremounted on a board so as to form an electrical circuit. This module isgenerally formed by mounting necessary components on one or bothsurfaces of a daughter board. However, when a technique which includesmounting components on a surface of a board is employed, a surface areaof the module cannot be smaller than those of the mounted components(that is, the total foot prints of the components). For this reason,there is a limitation to high-density assembly, even when this techniqueis employed. Further, since the components are disposed on a flatsurface according to the technique, a connection distance between thecomponents is inevitably longer depending on its constitution, whichresults in a problem of increase in loss and increase in inductance at ahigh frequency.

[0004] In order to eliminate or alleviate such a problem, a module isproposed wherein components are arranged not only two-dimensionally bybeing mounted on a surface of a board, but also three-dimensionally bybeing disposed inside the board. See Japanese Patent Kokai (Laid-Open)Publication No. 11(1999)-220262(A). This publication discloses a modulewith a built-in circuit component which includes an electricallyinsulating substrate formed of a mixture comprising 70 wt % to 95 wt %of an inorganic filler and a thermosetting resin, a plurality of wiringpatterns formed on at least a principal plane of the electricallyinsulating substrate, at least one active and/or passive componentarranged in an internal portion of the electrically insulating substrateand electrically connected to the wiring patterns, and an inner viaformed in the electrically insulating substrate for electricallyconnecting the wiring patterns. By constituting such a module,high-density can be achieved by three-dimensional connection, and theloss and inductance can be reduced by a shortened wiring length.

[0005] A capacitor is included in main components for constituting thefunctional module. Recently, as an electronic equipment is increasinglydigitalized and operates at a higher speed, it is strongly required thatthe capacitor used therefor has a large capacitance and a low impedance.

[0006] Conventionally, as the capacitors, an electrolytic capacitor inwhich a valve metal such as aluminum or tantalum is used, and amultilayer ceramic capacitor in which Ag/Pd or Ni is used for electrodesand barium titanate is used as a dielectric, have been employed. Inaddition to these capacitors, a solid electrolytic capacitor in which acathode is made of an electrically conductive polymer has been used. Thesolid electrolytic capacitor is preferably used, since it has a largecapacitance per unit volume and it is of a thin thickness whereby theheight of the module can be reduced.

[0007] A configuration of the solid electrolytic capacitor is describedbelow. The solid electrolytic capacitor contains a capacitor elementwhich includes a valve metal element for an anode (herein referred toanode valve metal element), a dielectric oxide film formed on a surfaceof the anode valve metal element, a solid electrolyte layer formed onthe dielectric oxide film, and a charge collecting element for a cathodeformed on the dielectric oxide film. The anode valve metal element is,for example, an aluminum foil for an anode. This foil for an anode isusually subjected to a surface roughening treatment and the dielectricoxide film is formed on the treated surface. An electrically conductivepolymer layer made of polypyrrole, polythiophene, or polyaniline isformed as the solid electrolyte layer. Further, a carbon layer and an Agpaste layer are formed in the stated order, so that the chargecollecting element for a cathode is formed. An anode terminal and acathode terminal of lead frames are generally connected to thiscapacitor element. Further, the capacitor element is sealed with amolded resin, which results in the capacitor as the component. SeeJapanese Patent Kokai (Laid-Open) Publication No. 2002-198264(A).

[0008] For such a solid electrolytic capacitor, various attempts havebeen made to reduce an equivalent series resistance (hereinafterreferred to as ESR) of the capacitor, and a low equivalent seriesinductance (hereinafter referred to as ESL) which is due to an externalconnection terminal of the capacitor. In order to reduce the ESR, amaterial for the electrically conductive polymer and materials for thecarbon layer and the Ag paste layer have been developed. On the otherhand, the anode connection is made by, for example, welding the anode tothe lead flame. Therefore, the connection resistance of the anodeconnection is lower than that of the cathode connection. For thisreason, improving the anode connection is not employed so often as atechnique for reducing the ESR.

[0009] In case where the capacitor is embedded in the substrate, as thecapacitor is smaller in size, an advantage in terms of configurationsuch as miniaturization and higher-density of the module and anelectrical advantage such as a shortened wiring length and a lowimpedance are obtained more effectively. However, the capacitor of theabove-described configuration tends to be larger in size, since themolding resin and lead frames are disposed around the capacitor element.For this reason, such a capacitor package does not offer theseadvantages sufficiently. Therefore, an attempt to connect the capacitorelement three-dimensionally to the board has been made by embedding thecapacitor element directly in the board without using the molding resinand the lead frames.

[0010] When the capacitor is mounted on a wiring layer of apredetermined wiring pattern with solder, solder mounting which isconventionally employed for mounting a chip component cannot be employedsince the valve metal element for an anode is not wetted by the solder.Further, use of lead (Pb) is restricting from the viewpoint ofenvironmental protection, and therefore, Sn—Pb eutectic solder which hasbeen conventionally used is toward prohibition. As an alternative tothis, a solder material which does not contain Pb is developing. Themelting point of the Pb-free material is generally higher than that ofthe eutectic solder. As the melting point of the solder material ishigher, the capacitor element is more seriously damaged by heat that isapplied upon welding, which results in deterioration of the capacitorproperties. In order to avoid such disadvantage, a method for connectingthe capacitor to the wiring pattern with a Pb-free electricallyconductive adhesive is also employed.

[0011] However, when the anode of the capacitor and the wiring patternare connected with the electrically conductive adhesive (herein referredto as a conductive adhesive), there is a problem of increase inconnection resistance at the anode due to the dielectric oxide film onthe surface of the anode valve metal element, which makes it difficultto realize the low ESR. Further, since the surface of the valve metalelement is roughened, the conductive adhesive is absorbed into pores(that is, depressed portions) of the anode formed by the surfaceroughening treatment. This also presents a problem of increase inconnection resistance. Further, this presents a problem of deteriorationof the connection reliability because of a low bonding strength betweenthe anode and the conductive adhesive.

SUMMARY OF THE INVENTION

[0012] In order to solve these problems, the present invention providesan electrolytic capacitor in the form of element with a low ESR and alow height which can be connected to a wiring layer with a lowresistance and is suitable for being embedded in a circuit board, and amethod for producing the same. Further, the present invention provides amodule with a built-in capacitor of a small size, a low height and ahigh density which has a low ESL and high-frequency responsibility andcan be driven by a large current, and a method for producing the same.Furthermore, the present invention provides a module with a built-incapacitor which has an electrical function as a single package.

[0013] The present invention provides a capacitor comprising:

[0014] a valve metal element for an anode including a capacitor formingpart and an electrode lead part;

[0015] a dielectric oxide film provided on a surface of the valve metalelement for an anode;

[0016] a solid electrolyte layer provided on the dielectric oxide film;and

[0017] a charge collecting element for a cathode provided on the solidelectrolyte layer,

[0018] wherein at least one through hole is formed in the electrode leadpart of the valve metal element for an anode to expose core of the valvemetal element outside.

[0019] The capacitor of the present invention is characterized in thatat least one through hole is formed in the electrode lead part of thevalve metal element for an anode so that the core of the valve metalelement is exposed outside. Here, the “core” of the valve metal elementmeans a metal part of the valve metal element. In the electrolyticcapacitor of the present invention, the core of the valve metal elementis exposed outside on at least a part of the inner surface of thethrough hole. A portion where the core is exposed outside corresponds toa metal surface which is not oxidized or a surface of a thin oxide filmwhich is formed by natural oxidation. Therefore, the interfaceresistance of a connection area between the portion where the core isexposed outside and an electric conductor (such as a conductiveadhesive) is much smaller than that of a connection area between thedielectric oxide film and the electric conductor. For this reason, inthe present invention, the portion where the core is exposed outside(hereinafter, referred to as a “core-exposed portion”) serves as aconnection portion (or a connection terminal) of the anode. Therefore,the present invention can provide an electrolytic capacitor with highconnection reliability, in which a low connection resistance at theanode and a low ESR are low.

[0020] In the capacitor of the present invention, the through hole isfilled with an electrically conductive resin composition (hereinreferred to as conductive resin composition) containing metal powder anda thermosetting resin, which composition is connected to the core of thevalve metal element. The connection between the conductive resincomposition and the core of the valve metal element is made by cure ofthe thermosetting resin. In the capacitor of this constitution, thecore-exposed portion is covered with and electrically connected to theconductive resin composition. Therefore, in this capacitor, thecore-exposed portion of the valve metal element serves as the connectionportion through the conductive resin composition. Further, theconductive resin composition makes it possible to easily and reliablyprovide an electrical connection between the core of the valve metalelement and other member (for example, a wiring layer of a circuitboard). This is because the connection does not require the conductiveadhesive to be inserted into the through hole to contact with the innersurface of the hole. Therefore, the capacitor of this constitution has alower ESR and more improved reliability.

[0021] In the capacitor wherein the through hole is filled with theconductive resin composition, the diameter of the through hole ispreferably from 0.5 to 2 times the thickness of the valve metal elementfor an anode. When the diameter is in this range, the conductive resincomposition is easily injected and well retained in the through hole.When the diameter of the through hole is too large, the resincomposition within the hole may fall off the hole.

[0022] Alternatively, the electrolytic capacitor of the presentinvention preferably includes a single electrically conductive particle(herein referred to as conductive particle) or a single electricallyconductive fiber (herein referred to as conductive fiber) which contactswith at least a part of the core portion of the valve metal element inthe through hole. The conductive particle and the core-exposed portionare electrically connected at the contact area therebetween. Therefore,in this capacitor of this constitution, the core-exposed portion of thevalve metal element serves as the connection portion through theconductive particle or the conductive fiber which exists in the throughhole. The capacitor of this constitution is also easily connected toother member with the conductive adhesive since the conductive particleor the conductive fiber exists within the through hole. Therefore, thiscapacitor also has a lower ESR and more improved reliability.

[0023] It is preferable that the end portion(s) of the conductiveparticle or the conductive fiber disposed within the through holeextends slightly beyond a surface(s) of the electrode lead part whichsurface is to be connected to other member (such as a wiring board),which facilitates connecting the capacitor to, for example, a wiringlayer.

[0024] In the capacitor wherein the conductive particle or fiber isdisposed within the through hole, it is preferable that the particle orfiber pierces the electrode lead part, that is, the through hole isformed by piercing the electrode lead part with the particle or fiber.This constitution ensures more reliable electrical connection betweenthe conductive particle or fiber and the core of the anode valve metalelement, whereby more improved reliability is achieved.

[0025] In the capacitor of the present invention having the throughhole, it is preferable that at least one electrically conductiveparticle contacts with the core of the valve metal element for an anodein the electrode lead part. Here, “an electrically conductive particlecontacts with the core of the valve metal element for an anode” meansthat a part of the electrically conductive particle(s) pierces thedielectric oxide film formed on the surface of the valve metal elementfor an anode and reaches the core. The core which contacts with theconductive particle(s) can be electrically connected to other member(such as a wiring board) through the particle. That is, this conductiveparticle(s) as well as the core-exposed portion can serve as theconnection portion of the anode. Therefore, this constitution increasesthe area of the connection portion of the anode resulting in a lowerconnection resistance, and therefore an electrolytic capacitor of alower loss can be obtained.

[0026] In the above electrolytic capacitor wherein the conductiveparticle(s) contacts with the core of the anode valve metal element, itis preferable that at least a part of the particle(s) is coated with athermosetting resin. That is, it is preferable that the conductiveparticle(s) is fixed to the anode valve metal element with thethermosetting resin. This constitution improves a connection strengthbetween the conductive particle(s) and the anode valve metal element,and therefore gives an electrolytic capacitor which has a higherconnection stability and a higher reliability.

[0027] Alternatively, in the capacitor of the present invention havingthe through hole, it is preferable that an electrically conductive resincomposition containing metal powder and a thermosetting resin is appliedto a surface of the electrode lead part of the valve metal element foran anode. This constitution increases the area which contributes to theconnection of the anode to the other member (such as a wiring board),resulting in a lower connection resistance and a higher connectionreliability.

[0028] Further, the present invention provides a circuit board with abuilt-in capacitor wherein the electrolytic capacitor of the presentinvention is disposed within an electrically insulating layer, andconnected to a wiring layer with a conductive adhesive. “An electrolyticcapacitor is disposed within an electrically insulating layer” meansthat a part or the whole of the electrolytic capacitor is buried orembedded in the electrically insulating layer. This circuit board with abuilt-in capacitor includes a small-sized electrolytic capacitor whichdoes not have a molding resin and lead frames. Further, anode of theelectrolytic capacitor is connected to the wiring layer at thecore-exposed portion of the valve metal element, and the cathode isconnected to the wiring layer on a surface of the charge collectingelement for a cathode, through the conductive adhesive respectively. Asdescribed above, the electrolytic capacitor enables the anode to beconnected to the wiring layer with a low connection resistance.Therefore, the circuit board with a built-in capacitor of the presentinvention is characterized in that 1) its height is low, 2)miniaturization and higher-density of the board can be realized, and 3)it has a low ESR and a low ESL which enables high-frequency response andlarge-current driving of the board.

[0029] In the circuit board with a built-in capacitor of the presentinvention, wiring layers are placed on both surfaces (that is bothsides) of the electrically insulating layer and electrically connectedthrough an inner via(s) which is formed in the electrically insulatinglayer. This constitution makes it possible to connect two wiring layersthrough an inner via(s) at a desired position(s) and to shorten shortthe wiring length. Therefore, this constitution contributes tominiaturization, higher-density and a lower height of the circuit boardwith a built-in capacitor, and reduces the loss and inductance of thecircuit board.

[0030] In this specification, a “surface” with respect to a layer or asheet member is referred to a surface vertical to the thicknessdirection, unless otherwise specified.

[0031] In the circuit board with a built-in capacitor of the presentinvention, the electrically insulating layer within which the capacitoris disposed preferably contains an inorganic filler and a thermosettingresin. By selecting the inorganic filler optimally, the coefficient ofliner expansion, the thermal conductivity and the dielectric constant ofthe electrically insulating layer can be controlled, which results in acircuit board with a built-in capacitor which has a high reliability andis excellent in heat releasability and high-speed responsibility. Byselecting the thermosetting resin optimally, the coefficient of linerexpansion, the glass transition point, and the elastic modulus of theelectrically insulating layer can be controlled, which results in acircuit board with a built-in capacitor which has a high reliability.

[0032] The inner via(s) is preferably formed of a mixture containingelectrically conductive powder (herein referred to as conductive powder)and a thermosetting resin. The conductive powder is one which is made ofan electrically conductive material (specifically, a metal). Thethermosetting resin in a cured state constitutes the inner via. Such aninner via has high reliability, and therefore improves the connectionreliability of the circuit board as a whole.

[0033] When the circuit board of the present invention contains abuilt-in capacitor in which a through hole is filled with a conductiveresin composition in the electrode lead part of the anode valve metalelement, metal powder contained in the resin composition is preferablymade of the same material as that of the conductive filler contained inthe conductive adhesive. This reduces a resistance of the connectionportion between the electrode lead part of the capacitor anode and thewiring layer, and improves reliability. Similarly, when a conductiveresin composition is applied to the electrode lead part of the anodevalve metal element in the electrolytic capacitor, metal powdercontained in the resin composition is preferably made of the samematerial as that of the conductive filler contained in the conductiveadhesive. Similarly, when a conductive particle or fiber is disposed inthe through hole of the electrolytic capacitor, the particle or fiber ispreferably made of the same material as that of the conductive fillercontained in the conductive adhesive. Similarly, when at least oneconductive particle contacts with the core of the anode valve metalelement in the electrode lead part, the conductive particle ispreferably made of the same material as that of the conductive fillercontained in the conductive adhesive. In other words, a conductivecomponent which exists in the electrode lead part of the electrolyticcapacitor, and the conductive filler contained in the conductiveadhesive are preferably unified in terms of material.

[0034] When the circuit board with a built-in capacitor is of aconstitution having the inner via, the inner via is preferably disposedso that it aligns with the through hole formed in the electrolyticcapacitor. That is, the inner via and the through hole are preferablyplaced on one line. This constitution shortens the connection lengthbetween the electrolytic capacitor and the wiring layer, resulting in alower ESR and a lower ESL of the circuit board.

[0035] In the constitution wherein the inner via aligns with the throughhole of the electrolytic capacitor, in the case where the through holeof the anode valve metal element is filled with a conductive resincomposition, the conductive powder contained in the inner via ispreferably made of the same material as that of metal powder containedin the conductive resin composition. This reduces the connectionresistance between the electrode lead part of the anode in theelectrolytic capacitor and the inner via, resulting in improvement ofconnection reliability. Similarly, when a conductive resin compositionis applied to the electrode lead part of the anode valve metal elementin the electrolytic capacitor, metal powder contained in the resincomposition is preferably made of the same material as that of theconductive powder contained in the inner via. Similarly, when aconductive particle or fiber is disposed within the through hole of thecapacitor, the particle or fiber is preferably made of the same materialas that of the conductive powder contained in the inner via. Similarly,in the case where at least one conductive particle contacts with thecore of the anode valve metal element in the electrode lead part, theconductive particle is preferably made of the same material as that ofthe conductive powder contained in the inner via. In other words, aconductive component which exists in the electrode lead part of theelectrolytic capacitor, and the conductive powder contained in the innervia are preferably unified in terms of material.

[0036] In the circuit board with a built-in capacitor of the presentinvention, a semiconductor chip may be further included and electricallyconnected to the electrolytic capacitor disposed in the electricallyinsulating layer, and the wiring layer may be connected to an externalelectrode through the inner via formed in the electrically insulatinglayer. This circuit board with a built-in capacitor fulfills apredetermined function together with the semiconductor chip and otheroptional components, as a module. Herein, a “module” means a componentwhich can be added, deleted and substituted as one unit. The module is,for example, a memory module or a plug-in module. The semiconductor chipis, for example, a switching element or a microprocessor.

[0037] Alternatively, in the circuit board with a built-in capacitor ofthe present invention, at least one component selected from the group ofa semiconductor chip such as a switching element or a microprocessor,another capacitor and inductor may be disposed within the electricallyinsulating layer within which the electrolytic capacitor is disposed oranother electrically insulating layer, and the component may beelectrically connected to a wiring layer. Such a circuit board with abuilt-in capacitor fulfills a predetermined function as one module.

[0038] This configuration gives a circuit board with a built-incapacitor that serves as a miniature and thin functional module of highdensity which fulfills a function of an electrical circuit as a singlepackage. Further, this configuration wherein an element for forming anelectrical circuit is disposed within the board, gives a more miniatureand thinner circuit module. Furthermore, this configuration makes itpossible to shorten the wiring length of the entire circuit, resultingin a circuit module which has a low loss and a low stray capacitance anda low inductance. In addition, the module presents improved noiseimmunity, since an passive component can be disposed near thesemiconductor chip. Therefore, the present invention makes it possibleto obtain a circuit board with a built-in capacitor serving as a goodfunctional module, in which 1) miniaturization, 2) higher-density, 3)low-height, and 4) excellent high-speed responsibility are realized.

[0039] In the case where the semiconductor chip is a switching element,and an inductor is electrically connected to the semiconductor chip andthe capacitor, a circuit board with a built-in capacitor containing suchcomponents serves as a switching power supply module. That is, thecircuit board of this constitution may be identified as a switchingpower supply module including a switching element, a capacitor, and aninductor which are electrically connected, wherein:

[0040] the capacitor is of the present invention, and disposed within anelectrically insulating layer and connected to a wiring layer with anelectrically conductive adhesive;

[0041] the wiring layer is connected to an external electrode through aninner via(s) formed in the electrically insulating layer. The switchingpower supply module is preferably, for example, a DC/DC converter. Byusing the electrolytic capacitor of a large capacitance and a low heightin the switching power supply module, power density is increased, whileripple voltage is reduced. Further, by disposing the electrolyticcapacitor of the present invention within the electrically insulatinglayer, the power density can be further increased.

[0042] In the case where the semiconductor chip is a microprocessor, acircuit board with a built-in capacitor containing this chip serves as amicroprocessor module. That is, the circuit board of this constitutionmay be identified as a microprocessor module, wherein:

[0043] at least one microprocessor is electrically connected to acapacitor:

[0044] the capacitor is of the present invention, and disposed within anelectrically insulating layer and connected to a wiring layer with anelectrically conductive adhesive;

[0045] the wiring layer is connected to an external electrode through aninner via(s) formed in the electrically insulating layer. Alternatively,the circuit board with a built-in capacitor which is provided with amicroprocessor may be identified as a microprocessor module comprisingthe circuit board with a built-in capacitor of the present invention andat least one microprocessor, wherein the microprocessor is electricallyconnected to a wiring layer of the circuit board.

[0046] In this microprocessor module, the microprocessor is generallymounted on a surface of the circuit board with a built-in capacitor ofthe present invention. The microprocessor is preferably arranged so thatthe electrolytic capacitor of the present invention is placed just belowthe microprocessor. This arrangement makes it possible to reduce thearea occupied by the module. Further, this arrangement makes it possibleto shorten the distance between the microprocessor and the capacitor,resulting in a microprocessor module excellent in high-speedresponsibility.

[0047] In the above, the terms “metal powder” or “(electrically)conductive particle” refers to the conductive component contained in theelectrically conductive resin composition, the term “(electrically)conductive filler” refers to the conductive component contained in theelectrically conductive adhesive, and the term “(electrically)conductive powder” refers to the conductive component contained in theinner via. These are not necessarily different from each other, andthese have a commonality in that they serve to ensure theelectroconductivity of the composition or the mixture in which they areto be contained. Further, each of these is made of an electricallyconductive material. Therefore, it should be noted that a specific shapeand material of one of these components may be the same as those of oneor more other components.

[0048] The present invention also provides a method for producing theelectrolytic capacitor of the present invention. Specifically, thecapacitor of the present invention is produced by a method including:

[0049] producing an electrolytic capacitor unit by a method including:

[0050] (a) forming a dielectric oxide film by oxidizing a surface of avalve metal element for an anode which includes a capacitor forming partand an electrode lead part; and

[0051] (b) forming a solid electrolyte layer on the dielectric oxidefilm, followed by forming a charge collecting element for a cathode onthe solid electrolyte layer; and

[0052] (c) forming a through hole(s) in the electrode lead part of thevalve metal element for an anode of the obtained electrolytic capacitorunit to expose the core of the valve metal element. In thisspecification, the term “electrolytic capacitor unit” refers to a solidelectrolytic capacitor before the through hole(s) is formed, and thisterm is used to distinguish such a capacitor from the capacitoraccording to the present invention. The electrolytic capacitor unit maybe referred to as an “electrolytic capacitor” in terms of its functionas a capacitor.

[0053] Alternatively, the electrolytic capacitor of the presentinvention may be produced by a method including:

[0054] (a) forming a dielectric oxide film by oxidizing a surface of avalve metal element for an anode which includes a capacitor forming partand an electrode lead part;

[0055] (c) forming a through hole(s) in the electrode lead part of thevalve metal element for an anode to expose the core of the valve metalelement; and

[0056] (b) forming a solid electrolyte layer on the dielectric oxidefilm, followed by forming a charge collecting element for a cathode onthe solid electrolyte layer,

[0057] in this order (that is, the operations (a), (c) and (b) areperformed in the stated order).

[0058] Both of the above methods are characterized in that throughhole(s) is formed in the electrode lead part of the valve metal elementfor an anode of the electrolytic capacitor so as to expose the core ofthe valve metal element. The two methods are different in when thetrough hole(s) is formed. In the first method, the through hole(s) isformed after the solid electrolyte layer and the charge collectingelement for a cathode have been formed. In the second method, thethrough hole(s) is formed before the solid electrolyte layer and thecharge collecting element for a cathode are formed. The advantage of thefirst method is that the core is not oxidized even if a heat treatmentis conducted for polymerizing the electrolyte layer. The advantage ofthe second method is that a work piece is handled easily when formingthe through hole(s).

[0059] A method for producing a solid electrolytic capacitor generallyincludes the operations (a) and (b). Hereinafter, in order to clarifythe features of each production method of the present invention and toavoid a lengthy description, “forming a dielectric oxide film byoxidizing a surface of a valve metal element for an anode which includesa capacitor forming part and an electrode lead part” merely refers to as“the operation (a)”, and “forming a solid electrolyte layer on thedielectric oxide film, followed by forming a charge collecting elementfor a cathode on the solid electrolyte layer” merely refers to as “theoperation (b).”

[0060] The methods of the present invention further includes:

[0061] preparing an electrically conductive resin composition containingmetal powder and an uncured thermosetting resin;

[0062] filling with the electrically conductive resin the throughhole(s) formed in the electrode lead part of the valve metal element foran anode; and

[0063] connecting the electrically conductive resin composition to thecore of the valve metal element by a heat treatment. This method givesan electrolytic capacitor wherein the conductive resin composition isfilled into the through hole(s) and connected to the core of the valvemetal element for an anode.

[0064] It is preferable that this method further includes pressurizingthe electrode lead part of the valve metal element for an anode afterfilling the through hole(s) with the conductive resin composition. Byadding a pressurization step, the connection between the core of thevalve metal element for an anode and the conductive resin compositionbecomes stronger. The electrolytic capacitor produced in this mannergives a lower connection resistance between the electrode lead part andother member (specifically, a wiring board), and more improvedconnection reliability.

[0065] The present invention provides a method for producing anelectrolytic capacitor including:

[0066] producing an electrolytic capacitor unit by a method includingthe operations (a) and (b); and

[0067] disposing at least one electrically conductive particle withinthe electrode lead part of the valve metal element for an anode of theelectrolytic capacitor unit, by placing the particle on the electrodelead part and then pressurizing, the particle diameter being larger thanthe thickness of the valve metal element for an anode.

[0068] The present invention also provides a method for producing anelectrolytic capacitor including:

[0069] producing an electrolytic capacitor unit by a method includingthe operations (a) and (b); and

[0070] disposing at least one electrically conductive fiber within theelectrode lead part of the valve metal element for an anode of theelectrolytic capacitor unit,

[0071] the fiber being longer than the thickness of the valve metalelement for an anode.

[0072] The above two methods are characterized in that the through holeis formed in the electrode lead part of the valve metal element whilethe conductive particle or fiber is disposed within in the hole, byhaving the particle or fiber pierce the electrode lead part. Thisproduction method gives an electrolytic capacitor wherein the conductiveparticle or fiber closely contacts with the core of the valve metalelement.

[0073] Further, the present invention provides a method for producing anelectrolytic capacitor including:

[0074] producing an electrolytic capacitor unit by a method includingthe operations (a) and (b); and

[0075] forming a stack by stacking a plurality of the electrolyticcapacitor units in the thickness direction;

[0076] piercing the electrode lead parts of the valve metal elements foran anode of electrolytic capacitor units with at least one electricallyconductive fiber, the fiber being longer than the thickness of the stackof the electrolytic capacitor units; and

[0077] separating the stack into a piece of electrolytic capacitor bycutting the electrically conductive fiber.

[0078] This method makes it possible to have one or more electricallyconductive fibers pierces a plurality of electrode lead parts of thevalve metal elements of the electrolytic capacitor units, at a time.Therefore, according to this method, an electrolytic capacitor whereinan electrically conductive fiber is disposed within the electrode leadpart of the valve element can be produced with a higher productivity.

[0079] Any of the above-described methods for producing the electrolyticcapacitor may further include bringing at least one electricallyparticle into contact with the core of the valve metal element for ananode, by disposing the particle on the electrode lead part of the valvemetal element followed by pressurizing. In this operation, thepressurization is performed so that a part of each conductive particlepierces the dielectric oxide film on the electrode lead part and reachesthe core, and the other part is positioned above the surface of thedielectric oxide film, in other words, so that the particle is projectedfrom that surface. That is, the pressurization is performed so that apart of each conductive particle is buried in the electrode lead part.These additional operations make it possible to produce an electrolyticcapacitor wherein electrically conductive particle(s) contacts with thecore of the valve metal element for an anode at the electrode lead partin which the through hole(s) is formed.

[0080] Alternatively, any of the above-mentioned methods for producingthe electrolytic capacitor may further includes:

[0081] bringing at least one electrically conductive particles intocontact with the core of the valve metal element for an anode, bydisposing an electrically conductive resin composition containing theparticle(s) and an uncured thermosetting resin on the electrode leadpart of the valve metal element and then by pressurizing; and

[0082] bonding the electrically conductive resin composition to theelectrode lead part of the valve metal element for an anode by a heattreatment. The pressurization is performed in the same manner asdescribed above, so that a part of the electrically conductive particleis buried in the electrode lead part. These operations make it possibleto produce an electrolytic capacitor wherein conductive particle(s)contacts with the core of the valve metal element in the electrode leadpart in which the through hole(s) is formed, and fixed to the electrodelead part with a thermosetting resin.

[0083] Alternatively, any of the above-described methods for producingthe electrolytic capacitor may further include:

[0084] applying an electrically conductive resin composition containingmetal powder and a thermosetting resin to the electrode lead part of thevalve metal element for an anode; and

[0085] bonding the conductive resin composition to the electrode leadpart of the valve metal element for an anode by heat treatment. Theseoperations makes it possible to produce an electrolytic capacitorwherein a layer of an electrically conductive resin compositioncontaining metal powder and a thermosetting resin is formed on a surfaceof the electrode lead part wherein the through hole is formed.

[0086] In the case where the layer of the conductive resin compositionis formed on the electrode lead part of the valve metal element for ananode, the electrode lead part may be pressurized after the conductiveresin composition has been applied thereto. In that case, the conductiveresin composition can be bonded more strongly to the surface of theelectrode lead part. The heat treatment and the pressurization may beconducted at the same time.

[0087] It is possible to form a layer of the conductive resincomposition on a flat plate previously, and sandwich the electrode leadpart of the valve metal element for an anode by the plates so as totransfer the conductive resin composition to the electrode lead part. Inthat case, the conductive resin composition is applied by the transfer.The electrode lead part is preferably pressurized at the time of thetransfer in order to strengthen the adhesion of the conductive resincomposition. In the case where the diameter of metal powder contained inthe resin composition is larger than the thickness of the dielectricoxide film and a large pressure is applied, metal powder (i.e.particles) contacts with the core of the valve metal in the capacitor.

[0088] The present invention also provides a method for producing acircuit board with a built-in capacitor which includes:

[0089] preparing a first circuit board in which a wiring layer is formedin a predetermined wiring pattern on a surface of an electricallyinsulating layer;

[0090] preparing an electrically conductive adhesive containing anelectrically conductive filler and an uncured thermosetting resin;

[0091] preparing a sheet member formed of a thermosetting resincomposition containing an uncured thermosetting resin and an inorganicfiller, as an electrically insulating substrate;

[0092] applying the electrically conductive adhesive to a predeterminedposition of a surface of the wiring layer of the first circuit board;

[0093] fixing the electrolytic capacitor of the present invention to thefirst circuit board (strictly, to the wiring layer of the first circuitboard) by disposing the capacitor on the electrically conductiveadhesive and then by curing the adhesive through a heat treatment; and

[0094] forming an electrically insulating layer within which thecapacitor is disposed, by superposing the electrically insulatingsubstrate on the first circuit board to which the electrolytic capacitoris fixed and then by heating and pressurizing, that is, forming anelectrically insulating layer where the capacitor is built in. This is amethod for producing a circuit board with a built-in capacitor in whichan electrically insulating layer is formed on a first circuit board andthe electrically insulating layer covers an electrolytic capacitor (thatis, the capacitor is embedded in the electrically insulating layer), byfixing the capacitor to the first circuit board, and then superposing asheet-like electrically insulating substrate thereon followed by heatingand pressurization.

[0095] In the method for producing the circuit board with a built-incapacitor, the electrically insulating layer constituting the firstcircuit board is preferably formed of a thermosetting resin compositionwhich constitutes the electrically insulating substrate. When theelectrically insulating substrate and the first circuit board are madeof the same material, the internal stress which generates upon thelamination and incorporation of the electrically insulating substrate,can be reduced. Thereby, a circuit board with a built-in capacitor withhigh connection reliability can be obtained.

[0096] The present invention provides a method for producing a circuitboard with a built-in capacitor which includes:

[0097] preparing an electrically conductive adhesive containing anelectrically conductive filler and an uncured thermosetting resin;

[0098] preparing a sheet member formed of a thermosetting resincomposition containing an uncured thermosetting resin and an inorganicfiller, as an electrically insulating substrate;

[0099] applying the electrically conductive adhesive to a predeterminedposition of a surface of a metal foil;

[0100] fixing the electrolytic capacitor of the present invention to themetal foil by disposing the capacitor on the electrically conductiveadhesive and then by curing the adhesive through a heat treatment;

[0101] forming an electrically insulating layer within which thecapacitor is disposed, by superposing the electrically insulatingsubstrate on the metal foil to which the electrolytic capacitor is fixedand then by heating and pressurizing, and

[0102] patterning the metal foil so as to form a wiring layer in apredetermined wiring pattern. The metal foil is preferably a copperfoil.

[0103] In this production method, the electrolytic capacitor is fixed toa surface of the metal foil that is to be a wiring layer, and theelectrically insulating substrate is superposed thereon. That is, inthis production method, the step of disposing the electrolytic capacitorwithin the electrically insulating layer and the step of fabricating thecircuit board having the wiring layer and the electrically insulatinglayer are conducted at the same time. Therefore, this production methoddoes not require preparing a first wiring board previously, andtherefore, gives a more miniature and thinner circuit board with abuilt-in capacitor. Further, this production method makes it possible todispose the electrolytic capacitor adjacent to an external electrode ofthe circuit board, resulting in a circuit board with a built-incapacitor having an improved high-frequency responsibility.

[0104] The present invention also provides a method for producing acircuit board with a built-in capacitor which includes:

[0105] forming a wiring layer in a predetermined wiring pattern on onesurface of a releasable carrier;

[0106] preparing an electrically conductive adhesive containing anelectrically conductive filler and an uncured thermosetting resin;

[0107] preparing a sheet member formed of a thermosetting resincomposition containing an uncured thermosetting resin and an inorganicfiller, as an electrically insulating substrate;

[0108] applying the electrically conductive adhesive to a predeterminedposition of a surface of the wiring layer;

[0109] fixing the electrolytic capacitor of the present invention to thewiring layer on the carrier by disposing the capacitor on the appliedadhesive and then by curing the adhesive through a heat treatment;

[0110] forming an electrically insulating layer within which theelectrolytic capacitor is disposed, by superposing the electricallyinsulating substrate on the releasable carrier to which the electrolyticcapacitor is fixed and then by heating and pressurizing; and

[0111] exposing the wiring layer by removing the releasable carrier.This production method also does not require a first circuit board towhich the electrolytic capacitor is fixed, and therefore, enablesproduction of a more miniature and thinner circuit board with a built-incapacitor having an improved high-frequency responsibility.

[0112] In any of the above-described methods for producing a circuitboard with a built-in capacitor, the conductive adhesive is preferablyapplied by printing. Printing enables the conductive adhesive to beapplied precisely only to a desired position.

[0113] Further, in any of the above-described methods for producing acircuit board with a built-in capacitor, it is preferable that anelectrically insulating substrate is prepared wherein one or morethrough holes are formed in a predetermined position and the hole(s) isfilled with a via paste containing electrically conductive powder and athermosetting resin. The via paste is subjected to a heat treatment atan appropriate time (specifically, at the time when the electricallyinsulating substrate is superposed so as to form the electricallyinsulating layer) so that the thermosetting resin is cured to form aninner via. Therefore, this production method including this operation ofpreparing such a substrate makes it possible to produce a circuit boardwith a built-in capacitor wherein two wiring layers disposed on bothsurfaces of the electrically insulating substrate are connected asdesired.

[0114] In the case where the through hole(s) is formed in theelectrically insulating substrate and the hole(s) is filled with the viapaste, the electrolytic capacitor is preferably disposed within theelectrically insulating so that the via paste in the through holecontacts with the electrode lead part of the valve metal element for ananode of the capacitor. Thereby, the wiring layer placed on a surface ofthe electrically insulating substrate and the electrolytic capacitor areelectrically connected through the inner via, and therefore, it ispossible to produce a circuit board with a built-in capacitor whereinthe wiring length is shorter and a lower connection resistance isrealized.

[0115] The electrolytic capacitor of the present invention is an elementwhich does not have a molding resin and lead frames, and characterizedin that through hole(s) is formed in the electrode lead part of thevalve metal element for an anode to expose the core of the valve metal.The surface of the exposed core serves as a connection portion which canbe connected to other member (particularly, a wiring board) with a lowresistance. The electrolytic capacitor of the present invention providedwith such a connection portion is suitable for being connected to awiring layer of the wiring board using an electrically conductiveadhesive. Further, since the electrolytic capacitor of the presentinvention is in the form of element, this capacitor can constitute acircuit board with a built-in capacitor which has a low height and ahigh reliability, and presents a low connection resistance.

[0116] Further, by incorporating the electrolytic capacitor of thepresent invention together with other components into a circuit board, aminiature module containing built-in components at a high density isgiven. Although the area needed for setting the module with built-incomponents of the present invention is small, this module fulfills manyfunctions. Further, in this module, it is possible to shorten the wiringlength and to dispose a semiconductor chip adjacent to the electrolyticcapacitor, whereby the stray capacitance and the stray inductance arereduced. Therefore, the present invention gives a low-loss circuit boardwith a built-in component which functions as a desired circuit and hasan excellent high-speed responsibility.

BRIEF DESCRIPTION OF THE DRAWINGS

[0117] A more complete appreciation of the invention and many of theattendant advantages thereof will become readily apparent with referenceto the following detailed description, particularly when considered inconjunction with the accompanying drawings, in which:

[0118]FIG. 1 shows a sectional view of a conventional electrolyticcapacitor which corresponds to a fundamental electrolytic capacitor unitfor constituting an electrolytic capacitor of the present invention.

[0119] FIGS. 2(a) and 2(b) show a sectional view and a plan view of anembodiment of an electrolytic capacitor of the present invention,respectively;

[0120]FIG. 3 shows a sectional view of another embodiment of anelectrolytic capacitor of the present invention;

[0121]FIG. 4 shows a sectional view of further another embodiment of anelectrolytic capacitor of the present invention;

[0122]FIG. 5 shows a sectional view of still further another embodimentof an electrolytic capacitor of the present invention;

[0123] FIGS. 6(a) to 6(c) schematically show the steps for producing anelectrolytic capacitor of the present invention;

[0124]FIG. 7 shows a sectional view of another embodiment of anelectrolytic capacitor of the present invention;

[0125] FIGS. 8(a) to 8(d) schematically show sectional viewsillustrating the steps in an embodiment of a method for producing acircuit board with a built-in electrolytic capacitor of the presentinvention;

[0126] FIGS. 9(a) to 9(d) schematically show sectional viewsillustrating the steps in another embodiment of a method for producing acircuit board with a built-in electrolytic capacitor of the presentinvention;

[0127] FIGS. 10(a) to 10(d) schematically show sectional viewsillustrating the steps in further another embodiment of a method forproducing a circuit board with a built-in electrolytic capacitor of thepresent invention;

[0128] FIGS. 11(a) to 11(d) schematically show the steps in a method forproducing a module with built-in components of the present invention;

[0129]FIG. 12 is a graph illustrating ESR at 100 kHz of a wiring boardon which an electrolytic capacitor obtained in Example 1 is mounted;

[0130]FIG. 13 is a graph illustrating ESR at 100 kHz of a circuit boardwherein an electrolytic capacitor obtained in Example 1 is built-in;

[0131]FIG. 14 shows a schematic circuit diagram of the electric circuitof a switching power supply module of the present invention;

[0132]FIG. 15 shows a sectional view of an embodiment of a switchingpower supply module of the present invention; and

[0133]FIG. 16 shows a sectional view of an embodiment of amicroprocessor module of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0134] Hereinafter, embodiments of an electrolytic capacitor, a circuitboard with a built-in capacitor, and an embodiment of a module with abuilt-in component together with the production methods, are describedwith reference to the drawings.

[0135] The fundamental configuration of the present invention is a solidelectrolytic capacitor unit which includes a valve metal element for ananode including a capacitor forming part and an electrode lead part, adielectric oxide film provided on a surface of the valve metal elementfor an anode, a solid electrolyte layer provided on the dielectric oxidefilm, and a charge collecting element for a cathode provided on thesolid electrolyte layer. This corresponds to a conventional electrolyticcapacitor. An electrolytic capacitor of the present invention isconstituted by forming a through hole(s) in the electrode lead part ofthe valve metal element for an anode of this electrolytic capacitor unitso as to expose the core of the valve metal element outside.

[0136] A sectional view of the solid electrolytic capacitor whichcorresponds to the fundamental configuration of the present invention isshown in FIG. 1. In FIG. 1, numeral 10 denotes the valve metal elementfor an anode, numeral 10A denotes the capacitor forming part, andnumeral 10B denotes the electrode lead part. Numeral 11 denotes thedielectric oxide film, numeral 12 denotes the solid electrolyte layer,and numeral 13 denotes the charge collecting element for a cathode.Numeral 14 denotes an insulator which ensures the insulation between theanode and the cathode.

[0137] For example, a foil or a sintered body made of a materialselected from aluminum, tantalum and niobium may be used as the valvemetal element for an anode 10. Aluminum is preferably used, sincealuminum is available at a low cost and excellent in productivity.Surfaces of the valve metal element for an anode 10 are generallyroughened by electrolytic etching in order to increase the surface area.

[0138] An electrically conductive polymer such as polypyrrole,polythiophene, or polyaniline may be used for forming the solidelectrolyte layer 12. The solid electrolyte layer 12 preferably furthercontains a dopant so that the electroconductivity of the conductivepolymer is increased to reduce the resistance. As the dopant, an ionfrom arylsulfonic acid such as an alkylnaphthalene sulfonic acid andpara-toluenesulfonic acid, and an aryl phosphoric ion may be used.

[0139] As the charge collecting element for a cathode 13, an Ag pastelayer with a carbon layer as an adhesive layer, a foil of Cu, Ni or Al,or the metal foil with a carbon layer on a surface which is to contactwith the solid electrolyte layer 12, may be used.

[0140] The insulator 14 is preferably provided in order to ensure theinsulation between the anode and the cathode to prevent a short circuit.As the insulator 14, for example, polyimide, polyamide, polyphenyleneether (PPE), polyphenylene sulfide (PPS) or polyphenylene oxide (PPO)may be used.

[0141] In the solid electrolytic capacitor shown in FIG. 1, only oneelectrode lead part 10B for the anode is formed. The fundamentalconfiguration of the present invention may be a solid electrolyticcapacitor which has a three-terminal configuration wherein two electrodelead parts for the anode are provided, or a four-terminal configurationwherein both of anode and cathode have two electrode lead parts. Theembodiments described below are applicable to such capacitors.

[0142] (Embodiment 1)

[0143] An embodiment of the electrolytic capacitor of the presentinvention is shown in FIGS. 2(a) and 2(b). FIG. 2(b) is a plan view ofthe electrolytic capacitor shown in FIG. 2(a). In FIGS. 2(a) and 2(b),numeral 10C denotes core of the valve metal element for an anode 10, andnumeral 15 denotes a through hole. The inner exposed surface of thethrough hole 15 except for the portion of the dielectric oxide film 11corresponds to the core-exposed portion 10D. In FIG. 2, the referencenumerals which are identical to those used in FIG. 1 denote identicalmembers or components described with reference to FIG. 1. Therefore, asto those members or components, the detailed description is omitted.

[0144] A method for producing the electrolytic capacitor of thisembodiment is described with reference to FIG. 2. Firstly, a metal foilfor the valve metal element for an anode is prepared. Herein, a casewhere an aluminum foil is used, is exemplified.

[0145] Firstly, the aluminum foil is subjected to electrolytic etchingin an electrolytic solution which mainly contains hydrochloric acid, byapplying alternating current to the Al foil. Thereby, surfaces of thealuminum foil are roughened to give the valve metal element for an anode10 with fine concavities and convexities on the surfaces, as shown inFIG. 2(a). Next, the valve metal element for an anode 10 is subjected toanodic oxidation so that the dielectric oxide film 11 with a desiredpressure resistance is formed on the surfaces. The dielectric oxide film11 is generally formed into a thickness in the range of 1 to 20 nm.However, the thickness of the dielectric oxide film 11 is not limited tothis range, and it is selected depending on the desired properties ofthe electrolytic capacitor. Next, a conductive polymer such aspolypyrrole, polypyrrole, polythiophene, or polyaniline is formed bychemical polymerization or the combination of chemical polymerizationand electrolytic polymerization, using a solution containing a dopantand a monomer. During the polymerization, the valve metal element for ananode 10 is masked except for the capacitor forming part 10A. Theconductive polymer layer corresponds to the solid electrolyte layer 12.

[0146] Next, on both surfaces of the valve metal element for an anode10, an insulator 14 is disposed at a border between the capacitorforming part 10A on which the solid electrolyte layer 12 is formed andthe electrode lead part 10B. The insulator 14 is formed by bonding atape of an appropriate electrically insulating material (such as apolyimide film) to the valve metal element. Subsequently, a carbon pasteis applied to the surfaces of the solid electrolyte layer 12, followedby being cured. Next, an Ag paste is applied on the carbon paste layer,followed by being cured by heating. These carbon layer and Ag pastelayer serve as the charge collecting element for a cathode 13. Thecarbon paste and Ag paste are applied by, for example, dipping.Alternatively, the charge collecting element for a cathode 13 may beformed by laminating a metal foil such as a Cu, Ni, or Al foil. In thatcase, the metal foil is bonded to the solid electrolyte layer 12 usingthe carbon paste.

[0147] Next, defect repair treatment of the dielectric oxide film 11 andthe insulating treatment of the solid electrolyte layer 12 areconducted. Specifically, the treatments are conducted by applying apredetermined voltage in a high-temperature and high-humidity atmosphere(for example, 85° C. and 80% RH), followed by drying. When thetreatments are completed, the electrolytic capacitor of theconfiguration shown in FIG. 1 is obtained.

[0148] Next, the through hole 15 is formed in the electrode lead part10B of the valve metal element for an anode so that the unoxidized core10C of the valve metal element for an anode is exposed outside, wherebythe electrolytic capacitor of the present invention having thecore-exposed portion 10D as shown in FIG. 2(a) can be obtained. Thethrough hole 15 may be formed using, for example, a NC punching machine.Alternatively, the through hole 15 may be formed by a method wherein apunching die is used, or by a YAG laser. The diameter of the throughhole 15 is, for example, from 30 to 300 μm. However, the size of thethrough hole 15 is not limited to this range. Further, a plurality ofthrough holes 15 are preferably formed. FIG. 2(b) shows an electrolyticcapacitor wherein three through holes 15 are formed, as one example. Asthe number of the through holes 15 is increased, the capacitor isconnected to a wiring layer with a lower connection resistance,resulting in a low-loss circuit board with a built-in capacitor and alow-loss module with a built-in components, and an improved connectionreliability. However, as the number of the through holes 15 isincreased, the strength of the electrode lead part 10 becomes lower.Therefore, it is necessary to select the number of the through holes 15so that the electrolytic capacitor is not broken by a force which isapplied upon producing the circuit board with a built-in capacitor.Generally, the number of the through holes 15 is preferably in the rangeof 1 to 8 per 1 mm².

[0149] In the above-described method, the through hole 15 is formed inthe electrode lead part 10B of the valve metal element for an anode 10after the electrolytic capacitor as shown in FIG. 1 has been fabricated.Alternatively, the through hole 15 may be formed after the dielectricoxide film 11 has been formed, and thereafter the solid electrolytelayer 12 and the charge collecting element for a cathode 13 may beformed. In such a method, since the through hole is formed before theelectrolytic capacitor unit is completed, a workpiece can be handledwithout concern about the damage of the solid electrolyte layer and soon when forming the through hole.

[0150] (Embodiment 2)

[0151] Another embodiment of the electrolytic capacitor of the presentinvention is shown in FIG. 3. In FIG. 3, numeral 16 denotes anelectrically conductive resin composition containing metal powder and athermosetting resin, which resin fills the through hole 15 and iselectrically connected to the core 10C of the valve metal element for ananode 10. In FIG. 3, the reference numerals which are identical to thoseused in FIGS. 1 and 2 denote identical members or components describedwith reference to FIGS. 1 and 2. Therefore, as to those members orcomponents, the detailed description is omitted.

[0152] A method for producing the electrolytic capacitor of thisembodiment is described with reference to FIG. 3. Firstly, theelectrolytic capacitor with the through hole as shown in FIG. 2 isfabricated by the method as described in connection with Embodiment 1.

[0153] Metal powder and a thermosetting resin are mixed to give anelectrically conductive resin composition. The metal powder ispreferably made of a metal that is excellent in conductivity andstability. For example, a metal or an alloy powder of which majorcomponent is Ag, Cu, Au, Ni, Co or Pd may be preferably used.Particularly, Ag or Cu powder, or powder made by an alloy containing Agor Cu may be preferably used. The diameter of the metal powder ispreferably in the range of 0.1 to 100 μm. The thermosetting resin in anuncured state is mixed with the metal powder. For example, an epoxyresin, a phenol resin or a polyimide resin can be used as thethermosetting resin. These resin is preferably used because of highreliability. The uncured thermosetting resin is preferably mixed in anamount of 30 to 150 parts by volume with the 100 parts by volume of themetal powder. Further, the conductive resin composition may furthercontain a curing agent, a curing catalyst, a surface active agent and/ora coupling agent.

[0154] Next, the through hole 15 is filled with the conductive resincomposition. A method for filling the through hole includes, forexample, a method employing a screen printing and a method employing adispenser. The conductive resin composition 16 is then connected to thecore 10C of the valve metal element for an anode 10 in the through hole15, by heat treatment for curing the thermosetting resin in the resincomposition 16. As a result, the electrolytic capacitor of the presentinvention as shown in FIG. 3 is obtained.

[0155] The temperature and time for the heat treatment are not limitedto particular ones as long as the properties of the capacitor is notdeteriorated due to thermal decomposition of the solid electrolyte layer12. The heat treatment temperature is generally in the range of 80 to180° C., and the heat treatment time is generally in the range of 5 to30 minutes. After completing this heat treatment, the treatments forrepairing the defection in the dielectric oxide film 11 and insulatingthe solid electrolyte layer 12 are preferably performed.

[0156] In this embodiment, the diameter of the through hole 15 ispreferably from 0.5 to 2 times the thickness of the valve metal elementfor an anode 10. The reason is as described above. The valve metalelement for an anode 10 is preferably formed of a metal foil of athickness of 40 to 150 μm in order to reduce the height of the circuitboard with a built-in capacitor. Therefore, when the metal foil of sucha thickness is used, the diameter of the through hole is selected fromthe range of 20 to 300 μm depending on the thickness of the foil.

[0157] The cross-sectional shape of the through hole 15 is not limitedto circle, and may be any of square, rectangular, and oval. When thecross-sectional shape of the through hole 15 is not circle, thepreferable size of the through hole is defined by a minimum value and amaximum value of the diametrical distance between two arbitrary pointson the outline of the cross-section of the through hole. Specifically,the minimum value is preferably longer than 0.5 times the thickness ofthe valve metal element for an anode, and the maximum value ispreferably is less than 2 times the thickness of the valve metal elementfor an anode. Further, also in this embodiment, a plurality of throughholes 15 may be formed and filled with the conductive resin composition.

[0158] Furthermore, in this embodiment, it is preferable that theelectrode lead part 10B of the valve metal element for an anode 10 ispressurized after the through hole 15 has been filled with theconductive resin composition 16. This pressurization step strengthensthe connection of the metal powder contained in the conductive resincomposition 16 in the through hole 15 to the core 10C, resulting in thereduction of the connection resistance. A pressurization method is notlimited to a particular one. The pressurization may be conducted, forexample, by pressing with flat plates, or by using compressed air. Thepressurization and the heat treatment may be conducted at the same time.

[0159] In this embodiment of the electrolytic capacitor, the conductiveresin composition serves as the connection portion of the anode, sincethe conductive resin composition contacts with the core of the valvemetal element for an anode. Therefore, the electrolytic capacitor ofthis embodiment can be easily connected to a wiring board withoutinserting, for example, an electrically conductive adhesive into thethrough hole.

[0160] (Embodiment 3)

[0161] Another embodiment of the electrolytic capacitor of the presentinvention is shown in FIG. 4. In FIG. 4, numeral 17 denotes anelectrically conductive particle. This conductive particle is disposedin the through hole 15 and contacts with the core 10C of the valve metalelement for an anode 10 to be electrically connected to the core. InFIG. 4, the reference numerals which are identical to those used inFIGS. 1 to 3 denote identical members or components described withreference to FIGS. 1 to 3. Therefore, as to those members or components,the detailed description is omitted.

[0162] A method for producing the electrolytic capacitor of thisembodiment is described with reference to FIG. 4. Firstly, the solidelectrolytic capacitor unit of the fundamental configuration as shown inFIG. 1 is fabricated by the method as described in connection withEmbodiment 1.

[0163] The conductive particle 17 is prepared of which diameter islarger than the thickness of the valve metal element for an anode 10.Next, the conductive particle 17 is disposed on the electrode lead part10B of the valve metal element for an anode 10, followed by beingpressurized so as to be disposed within the valve metal element for ananode 10, whereby the through hole 15 is formed and the conductiveparticle 17 contacts with the core of the valve metal element for ananode 10. As a result, the electrolytic capacitor as shown in FIG. 4 isobtained.

[0164] As the conductive particle 17, a particle of a high conductivityis used which has a hardness that enables the particle to pierce thevalve metal element for an anode 10 without the break of the particleupon pressurization. Specifically, a particle made of a metal or analloy of which main component is selected from Ag, Cu, Ni, Pd, Pt andAu, may be used. The conductive particle 17 has a diameter which islarger than the thickness of the valve metal element for an anode 10,and preferably has a diameter which is 1.0 to 1.2 times the thickness ofthe valve metal element for an anode 10, and more preferably has adiameter which is 1.05 to 1.2 times the thickness of the valve metalelement for an anode 10. In the case where the conductive particle ofsuch a diameter is disposed within the valve metal element for an anode,the upper and the lower end portions of the particle are projected fromthe surfaces of the capacitor, whereby the capacitor is advantageouslyconnected to other member (such as a wiring board). A pressurizationmethod is not limited to a particular one. For example, a pressing canbe employed for piercing the valve metal element for an anode with theconductive particle 17.

[0165] In the electrolytic capacitor of this embodiment, the conductiveparticle can serve as the connection portion of the anode, since theparticle contacts with the core of the valve metal element for an anode.Therefore, the electrolytic capacitor of this embodiment can be easilyconnected to a wiring board similarly to Embodiment 2.

[0166] The above-described method makes it possible to form the throughhole easily. In an alternative method, the through hole is previouslyformed as described in connection with Embodiment 1, and an electricallyconductive particle of which diameter is slightly larger than thediameter of the through hole is pressed into the through hole, wherebythe electrolytic capacitor as shown in FIG. 4 can be obtained.

[0167] As a variant of this embodiment, there is an embodiment wherein aplurality of conductive particles 17 are disposed within the valve metalelement for an anode 10 at a plurality of positions. The electrolyticcapacitor of such an embodiment enables the connection resistance to befurther reduced when connecting the capacitor to the wiring board.

[0168] (Embodiment 4)

[0169] Another embodiment of the electrolytic capacitor of the presentinvention is shown in FIG. 5. In FIG. 5, numeral 18 denotes anelectrically conductive fiber. This conductive fiber 18 is disposed inthe through hole 15 and contacts with the core 10C of the valve metalelement for an anode 10 to be electrically connected to the core. InFIG. 5, the reference numerals which are identical to those used inFIGS. 1 to 4 denote identical members or components described withreference to FIGS. 1 to 4. Therefore, as to those members or components,the detailed description is omitted.

[0170] A method for producing the electrolytic capacitor of thisembodiment is described with reference to FIG. 5. Firstly, the solidelectrolytic capacitor unit of the fundamental constitution as shown inFIG. 1 is fabricated by the method as described in connection withEmbodiment 1.

[0171] The conductive fiber 18 is prepared which is longer than thethickness of the valve metal element for an anode 10. Next, theconductive fiber 18 is made to pierce the electrode lead part 10B of thevalve metal element for an anode 10 so that the through hole 15 isformed and the conductive fiber 18 contacts with the core of the valvemetal element for an anode 10. As a result, the electrolytic capacitoras shown in FIG. 5 is obtained.

[0172] The conductive fiber 18 is made of a metal material which has ahigh conductivity and can be worked into a fiber or a thin wire.Specifically, as the conductive fiber 18, a fiber or a thin wire whichis obtained by working a metal or an alloy of which main component isselected from the group consisting of Ag, Cu, Ni, Pd, Pt, Au and Al, canbe used. The conductive fiber 18 has a length larger than the thicknessof the valve metal element for an anode 10, and preferably has a lengthwhich is 1.0 to 1.2 times the thickness of the valve metal element foran anode 10, and more preferably has a length which is 1.05 to 1.2 timesthe thickness of the valve metal element for an anode 10. In the casewhere the conductive fiber of such a length is disposed within the valvemetal element for an anode, the upper and the lower end portions of thefiber are projected from the surfaces of the capacitor, whereby thecapacitor is advantageously connected to other member (such as a wiringboard). The diameter of the conductive fiber 18 is preferably in therange of 20 to 200 μm. A method for making the conductive fiber 18pierce the valve metal element is not limited to a particular one. Theconductive fiber 18 can pierce the valve metal element for an anode bybeing pressurized by means of, for example, a pressing machine, a wirebonder or an ultrasonic.

[0173] In the electrolytic capacitor of this embodiment, the conductivefiber can serve as the connection portion of the anode, since the fibercontacts with the core of the valve metal element for an anode.Therefore, the electrolytic capacitor of this embodiment can be easilyconnected to a wiring board similarly to Embodiment 2.

[0174] The above-described method makes it possible to form the throughhole easily. In an alternative method, the through hole is previouslyformed as described in connection with Embodiment 1, and an electricallyconductive fiber with a diameter slightly larger than the diameter ofthe through hole and a length larger than the thickness of the valvemetal element for an anode is pressed into the through hole, whereby theelectrolytic capacitor as shown in FIG. 4 can be obtained.

[0175] As a variant of this embodiment, there is an embodiment wherein aplurality of conductive fibers 18 pierce the valve metal element for ananode 10 at a plurality of positions. The electrolytic capacitor of suchan embodiment enables the connection resistance to be reduced whenconnecting the capacitor to the wiring board.

[0176] (Embodiment 5)

[0177] Another method for producing the electrolytic capacitor ofEmbodiment 4 is described as Embodiment 5. In FIGS. 6(a) to 6(c), eachstep of the method is schematically shown in a sectional view. In FIG.6, the reference numerals which are identical to those used in FIGS. 1to 5 denote identical members or components described with reference toFIGS. 1 to 5. Therefore, as to those members or components, the detaileddescription is omitted.

[0178] Firstly, the solid electrolytic capacitor unit of the fundamentalconfiguration as shown in FIG. 1 is fabricated by the method asdescribed in connection with Embodiment 1. Next, a plurality of thesolid electrolytic capacitor units are stacked so that the surface (thatis, the surface which is vertical to the thickness direction of themetal foil that constitutes the valve metal element for an anode) isfaced with each other, in other words, they are stacked in the thicknessdirection thereof (FIG. 6(a)). Thereby, the electrode lead parts 10B ofthe valve metal elements for an anode 10 of the electrolytic capacitorunits coincide with each other (that is, align) in the thicknessdirection.

[0179] The conductive fiber 18 is prepared in the same manner as in theproduction of the electrolytic capacitor of Embodiment 4. In Embodiment5, it is required that the conductive fiber 18 has a length which islonger than that entire thickness d of the stack of the solidelectrolytic capacitor units. When the length of the conductive fiber 18is shorter than d, the conductive fiber 18 may not surely pierce eachelectrode lead part 10B of each valve metal element for an anode 10 ofeach electrolytic capacitor unit.

[0180] Next, as shown in FIG. 6(b), the conductive fiber 18 is made topierce the electrode lead parts 10B of the valve metal elements for ananode 10 of electrolytic capacitor units. The fiber is made to piercethe valve metal element by the method as described in connection withEmbodiment 4. Next, the conductive fiber 18 is cut at each positionbetween two electrode lead parts 10B of two valve metal elements for ananode 10 of two electrolytic capacitor units, so as to separate thecapacitor into a piece. As a result, the electrolytic capacitor as shownin FIG. 6(c) can be obtained.

[0181] Also in this embodiment, a plurality of conductive fibers maypierce at a plurality of positions in each electrolytic capacitor unit.Further, also in this embodiment, the through hole may be previouslyformed in each electrolytic capacitor unit, and a conductive fiber witha diameter slightly larger than that of the through hole may be made topierce this through hole. In that case, the through hole is formed ineach electrolytic capacitor at a time after the electrolytic capacitorunits have been stacked as shown in FIG. 6(a). Alternatively, theelectrolytic capacitors with a through hole are stacked so that thethrough holes coincide with each other, and then the fiber is made topierce the through holes.

[0182] In an alternative, the electrolytic capacitor of the embodimentas shown in FIG. 6(b) may be fabricated without cutting the conductivefiber, and may be used as a component for a circuit board. Theelectrolytic capacitor of such an embodiment has a large capacitancedepending on the number of the stacked electrolytic capacitors.Therefore, this production method is modified so as to obtain anelectrolytic capacitor of a desired capacitance by optimally selectingthe number of the solid electrolytic capacitor units of the fundamentalconfiguration.

[0183] (Embodiment 6)

[0184] Another embodiment of the electrolytic capacitor of the presentinvention is shown in FIG. 7. In FIG. 7, numeral 19 denotes anelectrically conductive particle. The electrolytic capacitor shown inFIG. 7 corresponds to the capacitor shown in FIG. 3 which furtherincludes the conductive particles 19 that contact with the core of thevalve metal element for an anode 10 over the electrode lead part 10B. InFIG. 7, the reference numerals which are identical to those used inFIGS. 1 to 6 denote identical members or components described withreference to FIGS. 1 to 6. Therefore, as to those members or components,the detailed description is omitted.

[0185] A method for producing the electrolytic capacitor of thisembodiment is described with reference to FIG. 7. Firstly, theelectrolytic capacitor as shown in FIG. 3 is fabricated by the method asdescribed in connection with Embodiment 2.

[0186] The conductive particles 19 are prepared and disposed on theelectrode lead part 10B of the valve metal element for an anode 10followed by being pressurized. Thereby, the conductive particles 19pierce the dielectric oxide film 11 formed on the valve metal elementfor an anode 10 to contact with the core 10C of the valve metal elementfor an anode 10. When a plurality of conductive particles 19 are used,it is not necessarily required that all of the conductive particlescontact with the core 10C of the valve metal element for an anode 10.The electrical connection between the core portion 10C and theconductive particle which does not contact with the core 10C isindirectly ensured, if this particle contacts with another particlewhich contacts with the core 10C. Further, the conductive particles 19preferably pierce the portion which has concavities and convexitiesresulted from the surface roughening treatment such as etching (that is,a roughened layer) so as to contact with a portion of the core whichportion is not affected by the surface roughening treatment. Theroughened layer is a region in the thickness direction which containsconcavities and convexities formed by the surface roughening treatment.When the valve metal element for an anode is cut in a directionperpendicular to the thickness direction in sequence, a cut surface ofthe valve metal element for an anode becomes a plane where concavitiesand convexities are not observed, in due time. This plane corresponds tothe border between the roughened layer and the portion which is notaffected by the surface roughening treatment. Generally, the thicknessof the roughened layer (that is, the distance in the thickness directionbetween the top of the highest convexity and the bottom of the deepestconcavity) is in the range of 20 to 100 μm.

[0187] As the conductive particle 19, for example, the particles asdescribed in connection with Embodiment 3 may be used. However,different from Embodiment 3, the conductive particles 19 pierce only thedielectric oxide film 11 and do not pierce the entire thickness of thevalve metal element for an anode 10. For this reason, it is preferablethat the conductive particle 19 has a diameter which is larger than thethickness of the dielectric oxide film 11 and is smaller than thethickness of the valve metal element for an anode 10. For example, whena plurality of conductive particles 19 are used, at least one conductiveparticle 19 preferably has a diameter of 30 to 70 μm. The conductiveparticle of such a diameter pierces the dielectric oxide film and theroughened layer to directly contact with the portion of the core 10C ofthe valve metal element for an anode 10 which portion is not affected bythe surface roughening treatment. When at least one particle has adiameter in the above range, the other particles have a diameter lessthan 30 μm, and may be in the range of 0.1 to 30 μm. However, it shouldbe noted that a specific and preferable range of particle diameterdepends on the thickness of the valve metal element for an anode and thethickness of the dielectric oxide film.

[0188] The conductive particles 19 are preferably disposed so that theycover the entire of both surfaces of the electrode lead part 10B, asshown in FIG. 7. Alternatively, the conductive particles 19 may bedisposed so as to cover the entire of one surface of the electrode leadpart 10B. Alternatively, the conductive particles 19 may be disposed soas to cover a part of one surface or a part of both surfaces of theelectrode lead part 10B.

[0189] In a variant of this embodiment, at least a part of theconductive particle is covered with a thermosetting resin. In a methodfor producing an electrolytic capacitor of such an embodiment, theconductive particles are mixed with an uncured thermosetting resin togive an electrically conductive resin composition, and the resincomposition is applied to the electrode lead part so as to dispose theconductive particles on the electrode lead part. The application isconducted by a printing, dipping, or a method wherein a dispenser isused. Next, the conductive particles are brought into contact with thecore of the valve element for an anode by pressurization, and then thethermosetting resin is cured by a heat treatment so that the resincomposition adheres to the electrode lead part. In the electrolyticcapacitor of this embodiment, since the conductive particles are fixedby the thermosetting resin more strongly, the conductive particles areless liable to fall out, resulting in higher connection reliabilitybetween the conductive particles and the core of the valve element foran anode. The thermosetting resin is not limited to a particular one.For example, an epoxy resin, a phenol resin, a polyimide resin, or anisocyanate resin may be used. The uncured thermosetting resin ispreferably mixed in an amount of 25 to 100 parts by volume withconductive particles of 100 parts by volume.

[0190] In an alternative method, the conductive resin compositioncontaining the conductive particles and the uncured thermosetting resinis applied to a desired position on a flat plate, and the electrode leadpart of the valve metal element for an anode is sandwiched by these twoplates so as to transfer the resin composition to the electrode leadpart. In that case, the conductive resin composition is applied by thetransfer. In that case, conductive particles can be brought into contactwith the core of the valve element for an anode by pressurizing theplates upon transferring the resin composition to the electrode leadpart. Further, the thermosetting resin is cured at the same time byconducting a heat treatment and the pressurization at the same time.Therefore, the transfer by means of plates is a preferable techniquesince the disposition (that is, application) of the conductive resincomposition and the fixation of the conductive particles can beconducted at the same time.

[0191] In the electrolytic capacitor shown in FIG. 7, the through hole15 is filled with the conductive resin composition. This embodiment isnot limited to one shown in FIG. 7, and may be applied to any of theembodiments shown in FIGS. 2, 4 and 5. In any case, the conductiveparticles may be previously brought into contact with the core of thevalve metal element for an anode, and then the through hole may be made,and further, the conductive resin composition may be optionally filledinto the through hole or the conductive particle or the conductive fibermay be optionally disposed within the through hole.

[0192] (Embodiment 7)

[0193] As Embodiment 7, a configuration in which the electrode lead partof the valve metal element for an anode is coated with an electricallyconductive resin composition containing metal powder and a thermosettingresin in the electrolytic capacitor as described in connection withEmbodiments 1 to 5, is described together with a method for producingthe capacitor of such a configuration.

[0194] The conductive resin composition as described in connection withEmbodiment 2 is preferably prepared also as the conductive resincomposition used for coating in this embodiment. Therefore, the detaileddescription is omitted.

[0195] The conductive resin composition is applied to a surface of theelectrode lead part of the valve metal element for an anode by anappropriate method. As an application method, a screen printing method,a dipping method or a method wherein a dispenser is used may beemployed. Thereafter, the conductive resin composition is subjected to aheat treatment so that the uncured thermosetting resin is cured and theresin composition adheres to the surface of the electrode lead part ofthe valve metal element for an anode. The temperature and time for headtreatment are not limited to particular ones, and the conditions asexemplified in connection with Embodiment 2 may be employed. When theelectrolytic capacitor of this embodiment is produced, the treatmentsfor repairing the defection in the dielectric oxide film and insulatingthe solid electrolyte layer are preferably performed in the same manneras in Embodiment 1 after the conductive resin composition resin has beenapplied.

[0196] Further, the electrode lead part of the valve metal element foran anode is preferably pressurized after the conductive resincomposition has been applied to the surface of the electrode lead part.By the pressurization, the adhesion strength and the electricalconnection between the conductive resin composition and the electrodelead part are improved.

[0197] In an alternative method, the conductive resin composition may beapplied to a desired position on a flat plate, and the electrode leadpart of the valve metal element for an anode is sandwiched by these twoplates so as to transfer the resin composition to the electrode leadpart, whereby the resin composition is applied. In that case, the flatplates may be pressurized upon transferring the resin composition to theelectrode lead part. Further, the pressurization and a heat treatmentmay be conducted at the same time, whereby the conductive resincomposition is applied and bonded to the electrode lead part at the sametime. In this manner, the transfer by means of plates has an advantagethat the application, the pressurization, and the heat treatment can beconducted in fewer steps.

[0198] (Embodiment 8)

[0199] As Embodiment 8, a method for producing a circuit board with abuilt-in capacitor using the electrolytic capacitor of the presentinvention is described. In FIGS. 8(a) to 8(d), each step of the methodis schematically shown in a sectional view.

[0200] Firstly, a summary of the procedures for producing the circuitboard with a built-in capacitor of the present invention is describedwith reference to FIG. 8. In the preparatory step, 1) a first circuitboard 22 with a wiring layer 21 in a predetermined wiring pattern on itssurface, and 2) an electrically conductive adhesive 23 containing anelectrically conductive filler and an uncured thermosetting resin areprepared. Further, 3) a sheet member formed of a thermosetting resincomposition containing an uncured thermosetting resin and an inorganicfiller is prepared as an electrically insulating substrate 25. In theelectrically insulating substrate 25, through hole 27 is optionallyformed in a desired position, and the through hole 27 is filled with avia paste 26 containing conductive powder and an uncured thermosettingresin.

[0201] The conductive adhesive 23 is applied to a desired position on asurface of the wiring layer 21 of the prepared first circuit board 22.Next, an electrolytic capacitor 24 of the present invention(corresponding to one shown in FIG. 3) is disposed on the conductiveadhesive 23, and then the adhesive 23 is cured by a heat treatment. As aresult, the electrolytic capacitor 24 is fixed and electricallyconnected to the wiring layer 21, as shown in FIG. 8(a).

[0202] Next, the electrically insulating substrate 25 and a copper foil28 are superposed on the first circuit board 22 to which theelectrolytic capacitor 24 is attached, as shown in FIG. 8(b), and then apressurization and a heat treatment are conducted. Thereby, as shown inFIG. 8(c), the electrically insulating substrate 25 adheres to thesurface of the first circuit board 22 to give an electrically insulatinglayer 29 and to dispose the electrolytic capacitor 24 within theelectrically insulating layer 29 (that is, to incorporate the capacitor24 into the electrically insulating layer 29). Further, by thesepressurization and heat treatment, the via paste 26 is cured to form aninner via 30. Next, the copper foil 28 is subjected to patterning toform a wiring layer 21 a in a predetermined wiring pattern, and therebythe circuit board with a built-in capacitor as shown in FIG. 8(d) iscompleted.

[0203] The first circuit board 22 is not limited to a particular one.For example, a printed-circuit board such as a glass-epoxy board, apaper-phenol board, and an aramid-epoxy board, and a ceramic board suchas an alumina board and a glass-alumina board can be used. A materialfor the wiring layer 21 is appropriately selected depending on the typeof the circuit board. For example, a copper foil may be used for theprinted-circuit board, and a sintered body formed of metal powder of Cu,Ag, Pd, Mo or W may be used for the ceramic board. The number of thewiring layers 21 contained in the first circuit board 22 is not limitedto a particular one. A multilayer circuit board as shown in FIG. 8 aswell as the double-faced circuit board wherein the wiring layer isformed only on both surfaces (that is, the number of the wiring layersare two), may be used.

[0204] In the first circuit board 22, the electrically insulating layersare preferably formed of the same material as that of the electricallyinsulating substrate 25. In the case where the material for theelectrically insulating layer is selected in this manner, theelectrically insulating layers in the finally obtained circuit boardwith a built-in capacitor are made of the same material, which enablesthe internal stress due to lamination of different materials to beeliminated or reduced. Thereby connection reliability of the circuitboard with a built-in capacitor is more improved.

[0205] The electrically conductive filler which constitutes theelectrically conductive adhesive 23 is not limited to a particular oneas long as it is a stable particle of a low specific resistance and alow contact resistance. Specifically, powder made of a metal or an alloyof which main component is Ag, Cu, Au, Ni, Pd or Pt may be used as theconductive filler. Particularly, Ag or Cu powder, or powder of an alloycontaining Ag or Cu is preferably used. As the uncured thermosettingresin which constitutes the conductive adhesive 23, for example, anepoxy resin, a phenol resin, a polyamide resin or a polyamide-imideresin may be used. These resins are preferably used because of highreliability. The thermosetting resin is preferably mixed in an amount of30 to 150 parts by volume with the conductive filler of 100 parts byvolume. The conductive adhesive 23 may further contain one or moreadditives selected from a curing agent, a curing catalyst, a surfaceactive agent, a coupling agent and a lubricant.

[0206] The conductive adhesive 23 is obtained by mixing the conductivefiller and the uncured thermosetting resin. As a mixing method, a methodusing three rolls, or a method using a planetary mixer may be employed.Alternatively, the commercially available conductive adhesive 23 may beused.

[0207] As a method for applying the conductive adhesive 23 to a desiredposition on the surface of the wiring layer 21 of the first circuitboard 22, a printing method or a method using a dispenser may beemployed. In terms of productivity, a metal mask printing method ispreferably employed. The heat treatment which follows the placement ofthe electrolytic capacitor 24 on the conductive adhesive 23 is conductedat a temperature at which the thermosetting resin contained in theadhesive can be cured. The heat treatment is preferably conducted at atemperature in the range of 80 to 180° C. for 5 to 30 minutes. When thetemperature is too high, the solid electrolyte layer in the electrolyticcapacitor is thermally decomposed to affect the properties of thecapacitor adversely.

[0208] The electrically insulating substrate 25 may be produced carryingout the following procedures. Firstly, a predetermined amount of theuncured thermosetting resin and an inorganic resin are metered andmixed. A mixing method is not limited to a particular one. For example,a method using a planetary mixer, a ball mill method using ceramicballs, or a method using a planetary stirring machine may be used. Next,the obtained thermosetting resin composition is worked into a sheet. Amethod for working the resin composition into a sheet is not limited toa particular one, and may be selected depending on the condition of thethermosetting resin composition. Specifically, a method using a doctorblade, an extrusion method, a method using a curtain coater, or a methodusing a roll coater may be employed. Particularly, the method using adoctor blade or the extrusion method is preferably employed because theyare simple.

[0209] The thermosetting resin contained in the electrically insulatingsubstrate 25 is, for example, an epoxy resin, a phenol resin, anisocyanate resin or a polyamide-imide resin. These resins are preferablyused because of high reliability. As the inorganic filler, a filler madeof, for example, Al₂O₃, SiO₂, SiC, AlN, BN, MgO or Si₃N₄ is preferablyused. Particularly, since the filler made of Al₂O₃ or SiO₂ is easilymixed with the thermosetting resin, the electrically insulatingsubstrate which is produced using such a filler can contain the fillerin a higher content. Further, in the case where the filler made ofAl₂O₃, SiC, or AlN is used, the thermal conductivity of the electricallyinsulating substrate 25 is improved, resulting in higher heatreleasability of the electrically insulating layer 29 in the circuitboard with a built-in capacitor. A mixture of two or more types offillers of different materials may be used as the inorganic filler. Aparticulate inorganic filler of which diameter is in the range of 0.1 to100 μm, is preferably used. In the material constituting theelectrically insulating substrate, the thermosetting resin is generallymixed in an amount of 20 to 200 parts by volume with the inorganicfiller of 100 parts by volume. However, the amount of the thermosettingresin is not limited to this range.

[0210] The electrically insulating substrate 25 may further contain oneor more additives selected from a curing agent, a curing catalyst, acoupling agent, a surface active agent, and a colorant. Further, theviscosity of the mixture may be adjusted by adding a solvent upon mixingthe inorganic filler and the thermosetting resin, depending on themethod for working the mixture into a sheet member. As the solvent usedfor adjusting the viscosity, methyl ethyl ketone (MEK), isopropanol ortoluene may be used. In the case where such a solvent is added, it isnecessary to remove the solvent by a drying treatment after thethermosetting resin composition has been worked into the sheet member.The drying treatment is not limited to a particular technique as long asthe treatment is conducted at a temperature below the curing-starttemperature of the thermosetting resin.

[0211] When the through hole 27 is formed in the electrically insulatingsubstrate 25, the through hole may be formed by means of, for example, aNC punching machine or carbon dioxide laser. Alternatively, the throughhole may be formed by a perforation method using a metal die.

[0212] The via paste 26 is made by mixing electrically conductive powderand the uncured thermosetting resin. They are mixed by the same methodas that employed for producing the conductive adhesive 23. As theconductive powder, powder made of a metal or an alloy of which maincomponent is Ag, Cu, Au, Ni, Pd or Pt, or an alloy thereof.Particularly, Ag or Cu powder, or powder of an alloy containing Ag or Cuis preferably used. As the uncured thermosetting resin, for example, anepoxy resin, a phenol resin, an isocyanate resin a polyamide resin or apolyamide-imide resin may be used. These resins are preferably usedbecause of high reliability. The thermosetting resin is preferably mixedin an amount of 30 to 150 parts by volume with the conductive powder of100 parts by volume. Further, a curing agent, a curing catalyst, alubricant, a coupling agent, a surface active agent, a high boilingsolvent and/or a reactive diluent may be further added to the via paste26.

[0213] A method for filling the though hole 27 with the via paste is notlimited to a particular one. For example, a screen printing method maybe applied.

[0214] In the step of FIG. 8(b), the temperature of pressurization andheating is properly selected so that the thermosetting resin containedin the electrically insulating substrate 25 can be cured and the solidelectrolyte layer of the electrolytic capacitor 24 is not adverselyaffected. The temperature is preferably in the range of 120 to 200° C.The pressurization and heating is conducted under a pressure which isproperly selected so that the electrolytic capacitor 24 is disposedwithin (i.e. buried in) the electrically insulating substrate 25, andthe electrically insulating substrate 25 becomes a layer adhering to thefirst circuit board 22 so as to make an electrical connection betweenthe wiring layer 21 and the copper foil 28 through the inner via 30. Thepressure is preferably selected from a range of 0.1 to 3 MPa.

[0215] The copper foil 28 constitutes the wiring layer 21 a in thefinally obtained circuit board with a built-in capacitor. The thicknessof the copper foil 28 is selected so that the wiring layer 21 a has adesired thickness. The thickness of the copper foil 28 is generally inthe range of 9 to 35 μm. A method for patterning the copper foil 28 isnot limited to a particular one. The copper foil is patterned, forexample, by a chemical etching using an aqueous solution of ironchloride or copper chloride. Another metal foil such as a nickel foil oran aluminum foil may be substituted for the copper foil 28 when needed.

[0216] In FIG. 8, the electrically insulating substrate 25 is a singlesheet member. In another embodiment, the electrically insulatingsubstrate 25 may be a laminate of the sheet members of the similar type.In that case, the thickness of the electrically insulating substrate 25can be adjusted as desired by selecting the number of the laminatedsheet members. Further, the electrically insulating substrate may besuperposed and subjected to a heating and pressurization treatment afteran unnecessary portion(s) has been removed (for example, cut away, ordrawn out) according to need. In that case, the position accuracy of theinner via is favorably improved.

[0217] In each step shown in FIG. 8, the electrolytic capacitor shown inFIG. 3 is used as the electrolytic capacitor 24. The built-inelectrolytic capacitor is not limited to this, and any of the capacitorsas described above may be used.

[0218] Particularly, when the electrolytic capacitor as shown in FIG. 3is used, it is preferable that the metal powder contained in theconductive resin composition 16 and the conductive filler contained inthe conductive adhesive 23 are made of the similar type of metal oralloy. In that case, the contact resistance between the conductive resincomposition 16 and the conductive adhesive 23 can be suppressed, and theconnection reliability is improved. Further, in the case where anelectrically conductive resin composition covers a surface of theelectrode lead part of the valve metal element for an anode in theelectrolytic capacitor, as described in Embodiment 8, it is preferablethat the metal powder contained in this resin composition and theconductive filler contained in the conductive adhesive 23 are made ofthe similar type of metal or alloy. In any case, the metal powder andthe conductive filler are preferably made of Cu, Ag, or an alloycontaining Cu or Ag.

[0219] In FIG. 8(b), the electrically insulating substrate 25 and thecopper foil 28 are superposed on the upper surface of the electrolyticcapacitor 24. In a variant of this embodiment, a second circuit board issubstituted for the copper foil 28. In that case, the patterning step ofFIG. 8(d) is not required. The configuration wherein the second circuitboard is superposed on the first circuit board makes it possible notonly to form an electrically insulating layer which includes a built-inelectrolytic capacitor, but also to form circuit patterns for rewiringabove and below the electrically insulating layer. Therefore, thisconfiguration is preferably employed since the circuit board with abuilt-in capacitor is designed more freely, and the wiring is containedat a higher density. As the second circuit board, a circuit boardsimilar to the first circuit board 22 shown in FIG. 8 may be employed.The second circuit board preferably has an electrically insulating layerwhich is composed of the same material as that of the electricallyinsulating substrate 25. Further, two circuit boards disposed above andbelow the electrolytic capacitor are preferably of the similar type, sothat warpage and internal stress which are caused upon fabricating thecircuit board with a built-in capacitor, can be reduced.

[0220] (Embodiment 9)

[0221] As Embodiment 9, another method for producing a circuit boardwith a built-in capacitor using the electrolytic capacitor of thepresent invention is described. In FIGS. 9(a) to 9(d), each step of themethod is schematically shown in a sectional view. In FIG. 9, thereference numerals which are identical to those used in FIG. 8 denoteidentical members or components described with reference to FIG. 8.Therefore, as to those members or components, the detailed descriptionis omitted.

[0222] The electrically conductive adhesive 23 and the electricallyinsulating substrate 25 which are prepared in the preparatory stage areas described in connection with Embodiment 8. In this embodiment, theelectrically insulating substrate 25 has the through hole 27 filled withthe via paste 26.

[0223] In this embodiment, the conductive adhesive 23 is applied to adesired position of a surface of the copper foil 28. Next, theelectrolytic capacitor 24 of the present invention (which corresponds toone shown in FIG. 1) is disposed on the conductive adhesive 23, and theconductive adhesive 23 is made to enter into the through hole 15followed by being cured by a heat treatment. As a result, theelectrolytic capacitor 24 is fixed and electrically connected to thecopper foil 28, as shown in FIG. 9(a).

[0224] Next, the electrically insulating substrate 25 and another copperfoil 28 a are superposed on the copper foil 28 to which the electrolyticcapacitor is attached, followed by being heated and pressurized, asshown in FIG. 9(b). Thereby, the electrically insulating layer 29 whichadheres to the copper foil 28 is formed and the electrolytic capacitor24 is disposed within (that is, incorporated into) the electricallyinsulating layer 29. Further, by this heating and pressurization, thevia paste is cured to form the inner via 30. Next, the two copper foils28 and 28 a are patterned into a predetermined wiring pattern to givewiring layers 21 and 21 a, whereby the circuit board with a built-incapacitor as shown in FIG. 9(d) is completed.

[0225] In this embodiment, there is no circuit board (which correspondsto the circuit board 22 in FIG. 8) for supporting the electrolyticcapacitor 24. For this reason, the thickness of the finally obtainedcircuit board with a built-in capacitor can come close to the thicknessof the electrolytic capacitor 24 itself, resulting in a low-heightcircuit board with a built-in capacitor. Further, in the circuit boardwith a built-in capacitor, since the distance between the electrolyticcapacitor 24 and the outermost wiring layer 21 is short, a lowerresistance and ESL are achieved, which makes it possible to realize anexcellent high-speed responsibility.

[0226] In FIG. 9, as the electrolytic capacitor 24, the capacitor ofEmbodiment 1 as described with reference to FIG. 2 is used. As shown inFIG. 9(a), the electrolytic capacitor 24 and the copper foil 28 areelectrically connected by the conductive adhesive 23 that enters intothe through hole 15 of the electrolytic capacitor 24 and contacts withthe core of the valve metal element for an anode. The electrolyticcapacitor 24 is not limited to this embodiment, and any of thecapacitors as described above may be used.

[0227] Further, in this embodiment, as shown in FIG. 9(b), theelectrically insulating substrate 25 is disposed so that the via paste26 contacts with the electrode lead part of the valve metal element foran anode of the electrolytic capacitor 24. As a result, the inner via 30is positioned just above the through hole 15 of the electrolyticcapacitor 24. By this configuration, the inner via 30 can be broughtinto direct contact with the electrode lead part of the electrolyticcapacitor 24 and with the conductive adhesive 23 via the through hole15, which enables the wiring to be shortened and the resistance to bereduced. In this configuration, the conductive powder contained in theinner via 30 and the conductive filler contained in the conductiveadhesive 23 is preferably made of the similar type of metal or alloy.

[0228] In the case where the electrolytic capacitor is any of theembodiments as shown in FIGS. 3 to 7, the conductive component locatedwithin the through hole (that is, the metal powder contained in theconductive resin composition, or the conductive particle or theconductive fiber), the conductive powder contained in the inner via andthe conductive filler contained in the conductive adhesive arepreferably made of the similar type of metal or alloy. In other words,in the connection region where the electrolytic capacitor and othercomponent or element are connected, it is preferable that the materialsof the conductive components are standardized or unified, whereby theresistance of the circuit board with a built-in capacitor is furtherreduced.

[0229] A method for producing the conductive adhesive 23, a method forapplying the conductive adhesive 23, a method for producing theelectrically insulating substrate 25, a method for forming the throughhole 27, a method for producing the via paste 26, a method for fillingthe through hole 27 with the via paste 26, and a method for patterningthe copper foils 28 and 28 a are as described above in connection withEmbodiment 8. Therefore, the detailed description thereof is omitted. Astack of the copper foil 28 a/the electrically insulating substrate25/the copper foil 28 is heated and pressurized by employing the methodfor heating and pressurizing the stack of the copper foil 28/theelectrically insulating substrate 25/the first circuit board 22 whichmethod is as described in connection with Embodiment 8.

[0230] (Embodiment 10)

[0231] As Embodiment 10, another method for producing a circuit boardwith a built-in capacitor using the electrolytic capacitor of thepresent invention is described. In FIGS. 10(a) to 10(d), each step ofthe method is schematically shown in a sectional view. In FIG. 10,numeral 31 denotes a releasable carrier. In FIG. 10, the referencenumerals which are identical to those used in FIGS. 8 and 9 denoteidentical members or components described with reference to FIGS. 8 and9. Therefore, as to those members or components, the detaileddescription is omitted.

[0232] Firstly, a summary of the procedures for producing the circuitboard with a built-in capacitor of the present invention is describedwith reference to FIG. 10. A copper foil is superposed on a surface of areleasable carrier 31A followed by being etched so as to form a wiringlayer 21A in a predetermined wiring pattern. Further, the electricallyconductive adhesive 23 is prepared in the same manner as in Embodiment8. Next, the conductive adhesive 23 is applied to a desired position ofthe surface of the wiring layer 21A formed on the releasable carrier31A. On the conductive adhesive 23, the electrolytic capacitor 24(corresponding to one shown in FIG. 7) is disposed, and thereafter theconductive adhesive 23 is cured by a heat treatment. As a result, theelectrolytic capacitor 24 is fixed and electrically connected to thewiring layer 21A, as shown in FIG. 10(a).

[0233] Next, the electrically insulating substrate 25 and anotherreleasable carrier 31B with a wiring layer 21B formed thereon aresuperposed on the releasable carrier 31A, as shown in FIG. 10(b),followed by being subjected to heating and pressurization. Thereleasable carrier 31B is disposed so that the wiring layer 21B contactswith the electrically insulating substrate 25. Thereby, as shown in FIG.10(c), the electrically insulating substrate 25 adheres to the wiringlayers 21A and 21B formed on the releasable carriers 31A and 31Brespectively, to form the electrically insulating layer 29, while theelectrolytic capacitor 24 is disposed within (that is, incorporatedinto) the electrically insulating layer 29. Further, by this heating andpressurization, the via paste 26 is cured to form the inner via 30.Thereafter, the releasable carriers 31A and 31B are removed so as toexpose the wiring layers 21A and 21B, whereby the circuit board with abuilt-in capacitor as shown in FIG. 10(d) is completed.

[0234] As the releasable carriers 31A and 31B, a sheet member whichenables a wiring layer to be formed on its surface and is not damaged bythe heating and pressurization treatment, is used. For example, a metalfoil such as a copper foil and an aluminum foil, and a film made of aresin such as polyphenylene sulfide (PPS), polyethylene terephthalate(PET), polyimide and polyethylene may be used as the releasable carriers31A and 31B.

[0235] The wiring layer 21A is formed on the surface of the releasablecarrier 31A by a method wherein an appropriate metal foil is superposedon the surface of the releasable carrier 31A and bonded to the carrierby pressurization and/or heating, followed by being subjected topatterning by etching. In this method, in order to increase the adhesionstrength between the releasable carrier and the metal foil, an adhesivelayer may be formed on the surface of the releasable carrier and themetal foil may be superposed on the adhesive layer. The adhesive layeris removed after the releasable carrier has been removed. Alternatively,the adhesive layer may be maintained on the releasable carrier andpeeled off together with the releasable carrier. The adhesive layer isformed of, for example, a silicone resin. Alternatively, the wiringlayer 21A is formed on the surface of the releasable carrier 31A or theadhesive layer, by plating the surface with an appropriate metal (suchas, copper) and patterning the plated metal by etching. The laminatewherein the wiring layer 21B is formed on the surface of the releasablecarrier 31B is formed in the same manner.

[0236] In this embodiment, there is no circuit board for supporting theelectrolytic capacitor 24 (which corresponds to the first circuit board22 in FIG. 8), similarly to Embodiment 9. Therefore, in the circuitboard obtained in this embodiment, the wiring length is shortened andthe height is lowered, resulting in improvement in the high-speedresponsibility of the circuit board. Further, in this embodiment, thewiring layer with a predetermined wiring pattern is previously formed onthe surface of the releasable carrier. For this reason, the circuitboard with a built-in capacitor which gives the above effects is moreeasily produced and a higher productivity is achieved. Furthermore, inthis embodiment, since the electrolytic capacitor is not affected by thepatterning step, the electrolytic capacitor is less damaged during theproduction of the circuit board. In addition, by employing the method ofthis embodiment, the surface of the wiring layer flushes with thesurface of the electrically insulating layer, which increases theadhesion strength between the wiring layer and the electricallyinsulating layer, and therefore, the wire is difficult to exfoliate.

[0237] The laminate wherein the wiring layer is formed on the surface ofthe releasable carrier can be called as a wiring transfer sheet and itis conventionally used in the production of the wiring board. In theproduction of the circuit board with a built-in capacitor of the presentinvention, the conventional wiring transfer sheet may be used as long asthe electrolytic capacitor of the present invention is bonded to thewiring layer with the conductive adhesive in the manner as describedabove.

[0238] A method for producing the conductive adhesive 23, a method forapplying the conductive adhesive 23, a method for producing theelectrically insulating substrate 25, a method for forming the throughhole 27, a method for producing the via paste 26 and a method forfilling the through hole 27 with the via paste 26 are as described abovein connection with Embodiment 8. Therefore, the detailed descriptionthereof is omitted. In the step of FIG. 10(b), a stack of the releasablecarrier 31B/the electrically insulating substrate 25/the releasablecarrier 31A is heated and pressurized by applying the method for heatingand pressurizing the stack of the copper foil 28/the electricallyinsulating substrate 25/the first circuit board 22 which method is asdescribed in connection with Embodiment 8.

[0239] (Embodiment 11)

[0240] As Embodiment 11, a module with a built-in component and a methodfor producing the same are described. In FIGS. 11(a) to 11(d), each stepof the method is schematically shown in a sectional view. In FIG. 11,numeral 41 denotes a semiconductor chip, numeral 42 denotes a chipcomponent, and numeral 43 denotes an inductor. In FIG. 11, the referencenumerals which are identical to those used in FIGS. 8 to 10 denoteidentical members or components described with reference to FIGS. 8 to10. Therefore, as to those members or components, the detaileddescription is omitted.

[0241] Firstly, the circuit board with a built-in capacitor 40 as shownin FIG. 8(d) is produced by the method of Embodiment 8. Next, thesemiconductor chip 41 and the chip component 42 are mounted on thewiring layer 21 a of this circuit board 40, as shown in FIG. 11(a).Next, as shown in FIG. 11(b), the electrically insulating substrate 25Aand the copper foil 28 are superposed on the circuit board with abuilt-in capacitor 40 on which the semiconductor chip 41 and the chipcomponents 42 are mounted, in the same manner as described in connectionwith Embodiment 8, and then subjected to heating and pressurization.This electrically insulating substrate 25A has a plurality of throughholes 27, and each of the through holes 27 are filled with the via paste26A.

[0242] By the heating and pressurization, the electrically insulatingsubstrate 25A is bonded to the circuit board 41 to form the electricallyinsulating layer 29A and the semiconductor chip 41 and the chipcomponents 42 are disposed within (that is, incorporated into) theelectrically insulating layer 29A. Further, by this heating andpressurization, the via paste 26A is cured to form the inner via 30A.This inner via 30A electrically connects the wiring layers 21 a and 21b. The wiring layer 21 b is a layer which is formed by patterning thecopper foil 28 into a predetermined wiring pattern.

[0243] Further, another semiconductor chip 41A and the inductor 43 aremounted on the wiring layer 21 b, whereby the module with a built-incomponent as shown in FIG. 11(d) is completed.

[0244] The semiconductor chip 41 is preferably mounted by a flip-chipmethod: By employing the flip-chip method, the module is advantageouslythinned, and the semiconductor chip 41 can be connected to the circuitboard with a wiring length shortened, whereby the high-speedresponsibility of the module with a built-in component is more improved.The built-in chip component 42 is not limited to a particular one. Forexample, a conventional chip resistor, chip capacitor and chip inductormay be built in as the chip component 42. Further, the chip componentmay be mounted using an electrically conductive adhesive, similarly tothe electrolytic capacitor, or using an alloy solder.

[0245] The module with a built-in component makes it possible to disposethe semiconductor chip and the chip component near the low-heightelectrolytic capacitor that is connected with a low resistance,resulting in an electric circuit of a low resistance, a low straycapacitance and a low inductance. Therefore, this module with a built-incomponent is of a low loss, and excellent in high-frequencyresponsibility. Further, many components can be mounted at a highdensity in this module, which enables the module to have a small areaand many functions.

[0246] In the configuration shown in FIG. 11, the semiconductor chip 41and the chip components 42 are disposed within the electricallyinsulating layer. The components disposed within the electricallyinsulating layer are not limited to these. For example, an inductorand/or one or more other capacitors may be disposed within theelectrically insulating layer.

[0247] (Embodiment 12)

[0248] As Embodiment 12, a switching power supply module of the presentinvention is described. In FIG. 14, a circuit of a DC/DC convertermodule which is one of the switching power supply modules of the presentinvention is schematically shown. In FIG. 14, the portion denoted bynumeral 51 corresponds to a switching element. Further, in FIG. 15, theswitching power supply module of the present invention is schematicallyshown in a sectional view. In FIG. 15, numeral 52 denotes a switchingelement. In FIG. 15, the reference numerals which are identical to thoseused in FIGS. 8 to 11 denote identical members or components describedwith reference to FIGS. 8 to 11. Therefore, as to those members orcomponents, the detailed description is omitted.

[0249] In the module shown in FIG. 15, the switching element 52, thechip component 42 and the inductor 43 are mounted on the wiring layer 21a of the circuit board with a built-in capacitor 40. In the embodimentshown in FIG. 15, the circuit board with a built-in capacitor 40 isfabricated by the method of Embodiment 8. The switching element 52 ispreferably mounted by a flip-chip method. The chip component 42 and theinductor 43 are mounted using an electrically conductive adhesive or analloy solder.

[0250] In the switching power supply module of this embodiment, theswitching element is placed near the electrolytic capacitor of a largecapacitance and a low height which is connected with a low resistance.For this reason, this switching power supply module can handle a largepower density, and operates at a low loss. Further, in the switchingpower supply module of this embodiment, the switching element and thecapacitor are connected with a wiring length shortened, resulting information of an electric circuit of a low inductance. Therefore, thisswitching power supply module is excellent in high-speed responsibility,and stable with a low ripple voltage.

[0251] In the embodiment shown in FIG. 15, only the electrolyticcapacitor 24 is disposed within the electrically insulating layer. Inanother embodiment, other components such as an inductor, a switchingelement and/or one or more other capacitors may be disposed within theelectrically insulating layer.

[0252] (Embodiment 13)

[0253] As Embodiment 13, a microprocessor module of the presentinvention is described. In FIG. 16, the microprocessor module of thepresent invention is schematically shown in a sectional view. In FIG.16, numeral 53 denotes a microprocessor, and numeral 54 denotes a chipcapacitor 54. In FIG. 16, the reference numerals which are identical tothose used in FIGS. 8 to 11 denote identical members or componentsdescribed with reference to FIGS. 8 to 11. Therefore, as to thosemembers or components, the detailed description is omitted.

[0254] In the microprocessor module of this embodiment, the chipcapacitor 54 is disposed within the electrically insulating layer 29Athat is placed above the wiring layer 21 a of the circuit board with abuilt-in capacitor 40, and the microprocessor 53 is mounted on thewiring layer 21 b formed on the electrically insulating layer 29A.Herein, the chip capacitor 54 serves as a decoupling capacitor, and itis properly selected depending on the frequency characteristics. Thechip capacitor 54 is preferably a ceramic capacitor.

[0255] The microprocessor module of this embodiment is produced asfollows. Firstly, the circuit board with a built-in capacitor 40 isfabricated by a method of Embodiment 8. Next, the chip capacitors 54 aremounted on the wiring layer 21 a. The chip capacitors 54 may be mountedusing an electrically conductive adhesive or an alloy solder. Next, anelectrically insulating layer 29A with a built-in chip capacitors 54 isformed by superposing an electrically insulating substrate and a copperfoil on the wiring layer 21 a followed by heating and pressurization inthe same manner as in Embodiment 11. The electrically insulatingsubstrate has through holes filled with the via paste. The via paste iscured by the heating and pressurization to form the inner via 30A thatconnects the wiring layers 21 a and 21 b. The wiring layer 21 b isformed by patterning the copper foil into a predetermined wiringpattern. Next, the microprocessor 53 is mounted on the wiring layer 21b, whereby the microprocessor module is obtained. The microprocessor 53is preferably mounted by a flip-chip method as shown in FIG. 16, becausethe flip-chip method is advantageous for thinning the module.Alternatively, the microprocessor 53 may be mounted by a wire bondingmethod.

[0256] As shown in FIG. 16, the microprocessor 53 is preferably disposedso that the electrolytic capacitor 24 is placed just below themicroprocessor 53. Thereby, the area required for setting the module canbe reduced. Further, this arrangement shortens the distance between themicroprocessor and the electrolytic capacitor, resulting in amicroprocessor module excellent in high-speed responsibility.

[0257] In the microprocessor module of this embodiment, themicroprocessor and the chip capacitors as decoupling capacitors aredisposed near the low-height electrolytic capacitor which is connectedwith a low resistance. For this reason, the microprocessor and thedecoupling capacitors can be connected with a low resistance and a lowinductance. Therefore, this microprocessor module is excellent inhigh-speed responsibility and stability of power input. Further, thisembodiment enables a plurality of capacitors to be mounted at a highdensity, resulting in a microprocessor module having a small area andhigh operation stability.

EXAMPLES

[0258] The following description will depict the present invention inmore detail, referring to examples, but the present invention is notlimited by the following examples.

Example 1

[0259] An aluminum foil with a thickness of 130 μm was prepared as anvalve metal element for an anode, and a surface of the foil wasroughened by electrolytic etching. The surface roughening was conductedby applying an alternating current to the aluminum foil in anelectrolytic solution containing hydrochloric acid mainly at aconcentration of 10 wt % at a liquid temperature of 35° C. The roughenedlayer thus formed had a thickness of 40 μm. Next, the aluminum foil wascut so that a 3 mm square region was formed. The square regioncorresponded to a capacitor forming part.

[0260] Next, the aluminum foil was subjected to constant voltageformation at a forming voltage of 8 V in a 5 wt % ammonium adipateaqueous solution at a liquid temperature of 60° C., so that thedielectric oxide film with a thickness of 7 nm was formed on surfaces ofthe valve metal element for an anode. Next, the capacitor forming partof the valve metal element for an anode was immersed in a solutioncontaining a polythiophene monomer, an iron-based oxidant and a dopant,so that the solid electrolyte layer was formed by chemicalpolymerization. Next, the dielectric oxide film was repaired byconducting anodic oxidation again in an organic-solvent-basedelectrolytic solution.

[0261] Subsequently, a polyimide tape with a width of 0.5 mm was affixedas an insulator on a border between the capacitor forming part and theelectrode lead part of the valve metal element for an anode, so that ananode portion was separated from the cathode portion. Next, a carbonpaste was applied to the solid electrolyte layer and heated, so that acarbon layer was formed. Further, an Ag paste layer was formed byapplying the Ag paste to the surface of the carbon layer, so that acharge collecting element for a cathode consisting of the carbon layerand the Ag paste layer was formed.

[0262] Next, the electrode lead part of the valve metal element for ananode was formed by punching with a punching die, so that a solidelectrolytic capacitor unit as shown in FIG. 1 with an outside dimensionof 3 mm×5 mm and a thickness of 0.23 mm was formed.

[0263] Ten through holes with a diameter of 0.15 mm were formed in theelectrode lead part of the valve metal element for an anode of theobtained solid electrolytic capacitor unit, by means of a NC punchingmachine. Thereby, an electrolytic capacitor as shown in FIG. 2 wasobtained.

[0264] For evaluating the obtained electrolytic capacitor, ten sampleswere fabricated and an ESR of each sample was determined. Each sampleincluded the electrolytic capacitor which was mounted on a glass-epoxywiring board. The electrolytic capacitor was mounted using anelectrically conductive adhesive which was made by kneading 82 wt % Agpowder and 18 wt % epoxy resin by means of three rolls. The wiring layerof the glass-epoxy board was formed into a wiring pattern adapted to theelectrode of the electrolytic capacitor. The mounting of theelectrolytic capacitor was conducted by printing the conductive adhesiveon a surface of the wiring layer using a metal mask, disposing theelectrolytic capacitor on the printed adhesive, and heating at 150° C.for 15 minutes. For comparison, a sample was fabricated by mounting theelectrolytic capacitor unit that did not have the through holes on theglass-epoxy board in the same manner. Ten samples for comparison wereprepared.

[0265] The ESR of each sample was determined by means of an impedancemeter (available from Agilent). The ESRs at 100 kHz are shown in FIG.12. As shown in FIG. 12, ESR of each sample containing the electrolyticcapacitor with through holes of the present invention was significantlysmaller than that of each sample for comparison. Further, the variationsin ESR from sample to sample were small as to the samples of the presentinvention. This result demonstrates that the electrolytic capacitor ofthe present invention is suitable to be mounted on a wiring board usingan electrically conductive adhesive.

[0266] Next, a circuit board with a built-in capacitor was fabricated bythe following procedures, and an ESR of the circuit board wasdetermined. Firstly, a solid component consisted of 81 wt % fused silicaand 19 wt % epoxy resin (including a curing agent) were kneaded with MEKas a solvent using a planetary mixer. The mixing weight ratio of solidcomponent to solvent was 10 to 1. This mixture was applied to a PETcarrier film by a method using a doctor blade, so that a film wasformed. Next, MEK was vaporized, so that a thermosetting sheet memberwith a thickness of 400 μm was formed.

[0267] Next, through holes with a diameter of 2 mm were formed in apredetermined positions of the sheet member by means of a punchingmachine. A via paste was made by kneading 87 wt % copper powder and 13wt % epoxy resin (including a curing agent) by means of three rolls.This via paste was filled into the through holes formed in the sheetmember by a printing method, so as to give an electrically insulatingsubstrate.

[0268] On the sample which had been previously fabricated by mountingthe electrolytic capacitor on the glass-epoxy board, the electricallyinsulating substrate and a copper foil with a thickness of 18 μm whereinone surface was roughened were superposed, and heated and pressurized at180° C. under 1 MPa. The copper foil was superposed so that theroughened surface was brought into contact with the electricallyinsulating substrate. After completing the heating and pressurization,the copper foil was etched with an iron chloride solution, so that acircuit board as shown in FIG. 8(d) was obtained. Ten circuit boardswere fabricated in this manner. For comparison, ten circuit boards werefabricated in the same manner using the samples which had beenfabricated for comparison.

[0269] An ESR of each sample was determined using the above-describedimpedance meter. The ESRs at 100 kHz are shown in FIG. 13. As shown inFIG. 13, ESR of each circuit board into which the electrolytic capacitorof the present invention was incorporated was small, and the variationsof ESRs were small as to these samples. On the other hand, ESR of eachcircuit board into which the electrolytic capacitor for comparison wasincorporated was increased due to the incorporation of the capacitor,and variations were large as to these comparative samples.

Example 2

[0270] An electrically conductive resin composition was made by kneading82 wt % Ag powder with a mean particle diameter of 12 μm and 18 wt %epoxy resin (including a curing agent) by means of three rolls. Thisconductive resin composition was filled into the through holes of theelectrolytic capacitor fabricated in Example 1, by a screen printingmethod. After filling, a heat treatment is conducted at 150° C. for 10minutes so as to bond the conductive resin composition to the exposedsurface of the through hole (that is, to fix the composition within thethrough hole), whereby an electrolytic capacitor as shown in FIG. 3 wasobtained. In Example 2, ten electrolytic capacitors were fabricated.

[0271] Each of these electrolytic capacitor was mounted on a glass-epoxyboard in the same manner as in Example 1. The mean ESR at 100 kHz ofthese ten samples was 60 mΩ. This value is significantly lower than eachof ESRs of the comparative samples shown in FIG. 12. Further, this valueis lower than the mean value of the samples of Example 1 shown in FIG.12. These results demonstrate that the through hole filled with theconductive resin composition is more advantageous for low-resistanceconnection.

[0272] Further, ten circuit boards were fabricated in the same manner asin Example 1 using this electrolytic capacitor. The mean ESR at 100 kHzof these circuit boards was 75 mΩ. This value is significantly lowerthan each of ESRs of the comparative samples shown in FIG. 13.

Example 3

[0273] The electrolytic capacitor unit as shown in FIG. 1 was producedin the same manner as in Example 1. Copper powder which was classifiedso that the diameter of each particle was at least 150 μm, was disposedon the electrode lead part of the valve metal element for an anode ofthis capacitor unit, and the electrode lead part was sandwiched withflat plates. Next, a pressure of 3 MPa was applied to the electrode leadpart through the plates so that the copper powder was disposed withinthe valve metal element for an anode, resulting in an electrolyticcapacitor as shown in FIG. 4. In one electrolytic capacitor, 10 to 15particles were disposed within the valve metal element for an anode. Inthis example, ten electrolytic capacitors were produced.

[0274] Each of these electrolytic capacitors was mounted on aglass-epoxy board in the same manner as in Example 1. The mean ESR at100 kHz of these ten samples was 55 mΩ. This value is significantlylower than each of ESRs of the comparative samples shown in FIG. 12.Further, this value is lower than that the mean value of the samples ofExample 1 shown in FIG. 12. These results demonstrate that theconfiguration wherein the conductive particle pierces the valve metalelement for an anode is more advantageous for low-resistance connection.

[0275] Further, ten circuit boards were fabricated in the same manner asin Example 1 using this electrolytic capacitor. The mean ESR at 100 kHzof these circuit boards was 65 mΩ. This value is significantly lowerthan each of ESRs of the comparative samples shown in FIG. 13.

Example 4

[0276] The electrolytic capacitor unit as shown in FIG. 1 was producedin the same manner as in Example 1. Six aluminum wires were made topierce the electrode lead part of the valve metal element for an anodeat six positions. Each wire has a diameter of 0.1 mm. Next, the aluminumwires were cut with a wire cutter so that both end portions of each wireextended beyond both surfaces of the electrode lead part, whereby anelectrolytic capacitor as shown in FIG. 5 was obtained. The length ofeach end portion was approximately 50 μm. In this example, tencapacitors were produced.

[0277] Each of these electrolytic capacitor was mounted on a glass-epoxyboard in the same manner as in Example 1. The mean ESR at 100 kHz of tensamples was 70 mΩ. This value is significantly lower than each of ESRsof the comparative samples shown in FIG. 12.

[0278] Further, ten circuit boards were fabricated in the same manner asin Example 1 using this electrolytic capacitor. The mean ESR at 100 kHzof these circuit boards was 80 mΩ. This value is significantly lowerthan that each of ESRs of the comparative samples shown in FIG. 13.

Example 5

[0279] The electrically conductive resin composition which was the sameas that used in Example 2 was prepared, and applied to a surface of aflat plate. The electrode lead part of the electrolytic capacitorproduced in Example 2 was sandwiched by two of such flat plates, and apressure of 30 MPa was applied to the electrode lead part so that theconductive resin composition was transferred to the electrode lead part.Next, a heat treatment was conducted at 150° C. for 30 minutes, to givean electrolytic capacitor as shown in FIG. 7. In this example, tencapacitors were produced.

[0280] Each of these electrolytic capacitor was mounted on a glass-epoxyboard in the same manner as in Example 1. The mean ESR at 100 kHz of tensamples was 65 mΩ. This value is significantly lower than each of ESRsof the comparative samples shown in FIG. 12.

[0281] Further, ten circuit boards were fabricated in the same manner asin Example 1 using this electrolytic capacitor. The mean ESR at 100 kHzof these circuit boards was 65 mΩ. This value is significantly lowerthan each of ESRs of the comparative samples shown in FIG. 13.

[0282] In the electrolytic capacitor of the present invention, thethrough hole formed in the electrode lead part of the valve metalelement for an anode gives an electrical connection part of a lowconnection resistance. Therefore, this electrolytic capacitor is usefulto produce a circuit board with a built-in capacitor, which board has asmall size, high density and a low height and a low ESR and can realizehigh-frequency response and large-current drive.

What is claimed is:
 1. An electrolytic capacitor comprising: a valvemetal element for an anode including a capacitor forming part and anelectrode lead part; a dielectric oxide film provided on a surface ofthe valve metal element for an anode; a solid electrolyte layer providedon the dielectric oxide film; and a charge collecting element for acathode provided on the solid electrolyte layer, wherein at least onethrough hole is formed in the electrode lead part of the valve metalelement for an anode to expose core of the valve metal element outside.2. The electrolytic capacitor according to claim 1, wherein the throughhole is filled with an electrically conductive resin compositioncontaining metal powder and a thermosetting resin, and the resincomposition is connected to the core of the valve metal element.
 3. Theelectrolytic capacitor according to claim 2, wherein a diameter of thethrough hole is from 0.5 to 2.0 times thickness of the valve metalelement for an anode.
 4. The electrolytic capacitor according to claim1, wherein a single electrically conductive particle or a singleelectrically conductive fiber is disposed within the through hole andthe particle or fiber contacts with at least a part of the core of thevalve metal element in the through hole.
 5. The electrolytic capacitoraccording to claim 4, wherein the single electrically conductiveparticle or the single electrically conductive fiber pierces theelectrode lead part of the valve metal element for an anode.
 6. Theelectrolytic capacitor according to claim 1, wherein at least oneelectrically conductive particle contacts with the core of the valvemetal element for an anode in the electrode lead part of the valve metalelement for an anode.
 7. The electrolytic capacitor according to claim6, wherein at least a part of the electrically conductive particle iscoated with a thermosetting resin.
 8. The electrolytic capacitoraccording to claim 1, wherein an electrically conductive resincomposition containing metal powder and a thermosetting resin is appliedto a surface of the electrode lead part of the valve metal element foran anode.
 9. A circuit board with a built-in capacitor comprising anelectrolytic capacitor which is disposed within an electricallyinsulating layer, and connected to a wiring layer with a conductiveadhesive, wherein the electrolytic capacitor comprises: a valve metalelement for an anode including a capacitor forming part and an electrodelead part; a dielectric oxide film provided on a surface of the valvemetal element for an anode; a solid electrolyte layer provided on thedielectric oxide film; and a charge collecting element for a cathodeprovided on the solid electrolyte layer, wherein at least one throughhole is formed in the electrode lead part of the valve metal element foran anode to expose core of the valve metal element outside.
 10. Thecircuit board with a built-in capacitor according to claim 9, whereinthe through hole formed in the electrolytic capacitor is filled with anelectrically conductive resin composition containing metal powder and athermosetting resin, and the resin composition is connected to the coreof the valve metal element.
 11. The circuit board with a built-incapacitor according to claim 10, wherein a diameter of the through holeis from 0.5 to 2.0 times thickness of the valve metal element for ananode.
 12. The circuit board with a built-in capacitor according toclaim 9, wherein a single electrically conductive particle or a singleelectrically conductive fiber is disposed within the through hole formedin the electrolytic capacitor, and the particle or fiber contacts withat least a part of the core of the valve metal element in the throughhole.
 13. The circuit board with a built-in capacitor according to claim12, wherein the single electrically conductive particle or the singleelectrically conductive fiber pierces the electrode lead part of thevalve metal element for an anode.
 14. The circuit board with a built-incapacitor according to claim 9, wherein at least one electricallyconductive particle contacts with the core of the valve metal elementfor an anode in the electrode lead part of the valve metal element foran anode of the electrolytic capacitor.
 15. The circuit board with abuilt-in capacitor according to claim 14, wherein at least a part of theelectrically conductive particle is coated with a thermosetting resin.16. The circuit board with a built-in capacitor according to claim 9,wherein an electrically conductive resin composition containing metalpowder and a thermosetting resin is applied to a surface of theelectrode lead part of the valve metal element for an anode of theelectrolytic capacitor.
 17. The circuit board with a built-in capacitoraccording to claim 9, wherein wiring layers are placed on both surfacesof the electrically insulating layer and electrically connected throughan inner via(s) which is formed in the electrically insulating layer.18. The circuit board with a built-in capacitor according to claim 9,wherein the electrically insulating layer comprises an inorganic fillerand a thermosetting resin.
 19. The circuit board with a built-incapacitor according to claim 17, wherein the inner via is formed of amixture of electrically conductive powder and a thermosetting resin. 20.The circuit board with a built-in capacitor according to claim 10,wherein the metal powder contained in the electrically conductive resincomposition that fills the through hole formed in the electrolyticcapacitor is made of the same material as that of an electricallyconductive filler contained in the electrically conductive adhesive. 21.The circuit board with a built-in capacitor according to claim 17,wherein the inner via is disposed so that it aligns with the throughhole formed in the electrolytic capacitor.
 22. The circuit board with abuilt-in capacitor according to claim 21, wherein the electricallyconductive powder contained in a mixture that constitutes the inner viais made of the same material as that of a metal powder contained in anelectrically conductive resin composition which fills the through holeformed in the electrolytic capacitor.
 23. The circuit board with abuilt-in capacitor according to claim 9, wherein: a semiconductor chipis further included, the semiconductor chip being electrically connectedto the electrolytic capacitor disposed within the electricallyinsulating layer; and the wiring layer is connected to an externalelectrode through the inner via formed in the electrically insulatinglayer.
 24. The circuit board with a built-in capacitor according toclaim 9, wherein at least one component selected from the groupconsisting of a semiconductor chip, another capacitor and inductor isdisposed within the electrically insulating layer within which theelectrolytic capacitor is disposed or within another electricallyinsulating layer, and the component is electrically connected to awiring layer.
 25. The circuit board with a built-in capacitor accordingto claim 23, wherein the semiconductor chip is a switching element or amicroprocessor.
 26. A switching power supply module comprising aswitching element, a capacitor, and an inductor which are electricallyconnected, wherein: the capacitor is an electrolytic capacitorcomprising: a valve metal element for an anode including a capacitorforming part and an electrode lead part; a dielectric oxide filmprovided on a surface of the valve metal element for an anode; a solidelectrolyte layer provided on the dielectric oxide film; and a chargecollecting element for a cathode provided on the solid electrolytelayer, wherein at least one through hole is formed in the electrode leadpart of the valve metal element for an anode to expose core of the valvemetal element outside, and the capacitor is disposed within anelectrically insulating layer and connected to a wiring layer with anelectrically conductive adhesive; and the wiring layer is connected toan external electrode through an inner via(s) formed in the electricallyinsulating layer.
 27. The switching power supply module according toclaim 26, which is a DC/DC converter.
 28. A microprocessor modulecomprising at least one microprocessor which is electrically connectedto a capacitor, wherein: the capacitor is an electrolytic capacitorcomprising: a valve metal element for an anode including a capacitorforming part and an electrode lead part; a dielectric oxide filmprovided on a surface of the valve metal element for an anode; a solidelectrolyte layer provided on the dielectric oxide film; and a chargecollecting element for a cathode provided on the solid electrolytelayer, wherein at least one through hole is formed in the electrode leadpart of the valve metal element for an anode to expose core of the valvemetal element outside, and the capacitor is disposed within anelectrically insulating layer and connected to a wiring layer with anelectrically conductive adhesive; and the wiring layer is connected toan external electrode through an inner via(s) formed in the electricallyinsulating layer.
 29. A microprocessor module comprising at least onemicroprocessor and a circuit board with a built-in capacitor in which anelectrolytic capacitor is disposed within an electrically insulatinglayer and electrically connected to a wiring layer, wherein: thecapacitor is an electrolytic capacitor comprising: a valve metal elementfor an anode including a capacitor forming part and an electrode leadpart; a dielectric oxide film provided on a surface of the valve metalelement for an anode; a solid electrolyte layer provided on thedielectric oxide film; and a charge collecting element for a cathodeprovided on the solid electrolyte layer, wherein at least one throughhole is formed in the electrode lead part of the valve metal element foran anode to expose core of the valve metal element outside, and themicroprocessor is electrically connected to the wiring layer of thecircuit board with a built-in capacitor.
 30. The microprocessor moduleaccording to claim 28, wherein the electrolytic capacitor is arrangedjust below the microprocessor.
 31. A method for producing anelectrolytic capacitor comprising: producing an electrolytic capacitorunit by a method including: forming a dielectric oxide film by oxidizinga surface of a valve metal element for an anode which includes acapacitor forming part and an electrode lead part; and forming a solidelectrolyte layer on the dielectric oxide film, followed by forming acharge collecting element for a cathode on the solid electrolyte layer;and forming a through hole(s) in the electrode lead part of the valvemetal element for an anode of the obtained electrolytic capacitor unit.32. A method for producing an electrolytic capacitor comprising: forminga dielectric oxide film by oxidizing a surface of a valve metal elementfor an anode which includes a capacitor forming part and an electrodelead part; forming a through hole(s) in the electrode lead part of thevalve metal element for an anode; and forming a solid electrolyte layeron the dielectric oxide film, followed by forming a charge collectingelement for a cathode on the solid electrolyte layer, in the statedorder.
 33. The method according to claim 31, which further comprises:preparing an electrically conductive resin composition containing metalpowder and an uncured thermosetting resin; filling with the electricallyconductive resin the through hole(s) formed in the electrode lead partof the valve metal element for an anode; and connecting the electricallyconductive resin composition to the core of the valve metal element by aheat treatment.
 34. The method according to claim 33, which furthercomprises pressurizing the electrode lead part of the valve metalelement for an anode after filling the through hole(s) with theelectrically conductive resin composition.
 35. The method according toclaim 31, wherein through hole(s) is formed by disposing at least oneelectrically conductive particle within the electrode lead part of thevalve metal element for an anode of the electrolytic capacitor unit, byplacing the particle on the electrode lead part and then pressurizing soas to pierce the electrode lead part with the particle, the particlediameter being larger than the thickness of the valve metal element foran anode.
 36. The method according to claim 31, wherein through hole(s)is formed by disposing at least one electrically conductive fiber withinthe electrode lead part of the valve metal element for an anode of theelectrolytic capacitor unit, the fiber being longer than thickness ofthe valve metal element for an anode.
 37. The method according to claim31, wherein: the through hole is formed by: forming a stack by stackinga plurality of the electrolytic capacitor units in a thicknessdirection; and piercing the electrode lead parts of the valve metalelements for an anode of electrolytic capacitor units with at least oneelectrically conductive fiber, the fiber being longer than the thicknessof the stack of the electrolytic capacitor units; and the stack isseparated into a piece of electrolytic capacitor by cutting theelectrically conductive fiber.
 38. The method according to claim 31,which further comprises bringing at least one electrically conductiveparticle into contact with the core of the valve metal for an anode, bydisposing the particle on the electrode lead part of the valve elementfor an anode followed by pressurization.
 39. The method according toclaim 31, which further comprises: bringing at least one electricallyconductive particles into contact with the core of the valve metalelement for an anode, by disposing an electrically conductive resincomposition containing the particle and an uncured thermosetting resinon the electrode lead part of the valve metal element followed bypressurization; and bonding the electrically conductive resincomposition to the electrode lead part of the valve metal element for ananode by a heat treatment.
 40. The method according to claim 31, whichfurther comprises: applying an electrically conductive resin compositioncontaining metal powder and a thermosetting resin to the electrode leadpart of the valve metal element for an anode; and bonding theelectrically conductive resin composition to the electrode lead part ofthe valve metal element for an anode by a heat treatment.
 41. A methodproducing a circuit board with a built-in capacitor comprising:preparing a first circuit board in which a wiring layer is formed in apredetermined wiring pattern on a surface of an electrically insulatinglayer; preparing an electrically conductive adhesive containing anelectrically conductive filler and an uncured thermosetting resin;preparing a sheet member formed of an thermosetting resin compositioncontaining an uncured thermosetting resin and an inorganic filler, as anelectrically insulating substrate; applying the electrically conductiveadhesive to a predetermined position of a surface of the wiring layer ofthe first circuit board; fixing an electrolytic capacitor to the firstcircuit board by disposing the capacitor on the applied adhesive andthen by curing the adhesive through a heat treatment; and superposingthe electrically insulating substrate on the first circuit board towhich the electrolytic capacitor is fixed, followed by heating andpressurization, so as to form an electrically insulating layer withinwhich the electrolytic capacitor is disposed, in which the electrolyticcapacitor is an electrolytic capacitor comprising: a valve metal elementfor an anode including a capacitor forming part and an electrode leadpart; a dielectric oxide film provided on a surface of the valve metalelement for an anode; a solid electrolyte layer provided on thedielectric oxide film; and a charge collecting element for a cathodeprovided on the solid electrolyte layer, wherein at least one throughhole is formed in the electrode lead part of the valve metal element foran anode to expose core of the valve metal element outside.
 42. Themethod according to claim 41, wherein the electrically insulating layerconstituting the first circuit board and the electrically insulatingsubstrate are formed of the same thermosetting resin composition.
 43. Amethod producing a circuit board with a built-in capacitor comprising:preparing an electrically conductive adhesive containing an electricallyconductive filler and an uncured thermosetting resin; preparing a sheetmember formed of a thermosetting resin composition containing an uncuredthermosetting resin and an inorganic filler, as an electricallyinsulating substrate; applying the electrically conductive adhesive to apredetermined position of a surface of a metal foil; fixing anelectrolytic capacitor to the metal foil by disposing the capacitor onthe applied adhesive and then by curing the adhesive through a heattreatment; superposing the electrically insulating substrate on themetal foil to which the electrolytic capacitor is fixed, followed byheating and pressurization, so as to form an electrically insulatinglayer within which the capacitor is disposed, and patterning the metalfoil so as to form a wiring layer in a predetermined wiring pattern, inwhich the electrolytic capacitor is an electrolytic capacitorcomprising: a valve metal element for an anode including a capacitorforming part and an electrode lead part; a dielectric oxide filmprovided on a surface of the valve metal element for an anode; a solidelectrolyte layer provided on the dielectric oxide film; and a chargecollecting element for a cathode provided on the solid electrolytelayer, wherein at least one through hole is formed in the electrode leadpart of the valve metal element for an anode to expose core of the valvemetal element outside.
 44. The method according to claim 42, wherein themetal foil is a copper foil.
 45. A method producing a circuit board witha built-in capacitor comprising: forming a wiring layer in apredetermined wiring pattern on one surface of a releasable carrier;preparing an electrically conductive adhesive containing an electricallyconductive filler and an uncured thermosetting resin; preparing a sheetmember formed of a thermosetting resin composition containing an uncuredthermosetting resin and an inorganic filler, as an electricallyinsulating substrate; applying the electrically conductive adhesive to apredetermined position of a surface of the wiring layer; fixing anelectrolytic capacitor to the releasable carrier by disposing thecapacitor on the applied adhesive and then by curing the adhesivethrough a heat treatment; superposing the electrically insulatingsubstrate on the releasable carrier to which the electrolytic capacitoris fixed, followed by heating and pressurization, so as to form anelectrically insulating layer within which the electrolytic capacitor isdisposed; and exposing the wiring layer by removing the releasablecarrier, in which the electrolytic capacitor is an electrolyticcapacitor comprising: a valve metal element for an anode including acapacitor forming part and an electrode lead part; a dielectric oxidefilm provided on a surface of the valve metal element for an anode; asolid electrolyte layer provided on the dielectric oxide film; and acharge collecting element for a cathode provided on the solidelectrolyte layer, wherein at least one through hole is formed in theelectrode lead part of the valve metal element for an anode to exposecore of the valve metal element outside.
 46. The method according toclaim 41, wherein as the electrically insulating substrate, anelectrically insulating substrate wherein one or more through holes areformed in a predetermined position and the hole(s) is filled with a viapaste containing electrically conductive powder and an uncuredthermosetting resin is prepared, and an inner via(s) is formed uponforming the electrically insulating layer by the heating andpressurization.
 47. The method according to claim 43, wherein as theelectrically insulating substrate, an electrically insulating substratewherein one or more through holes are formed in a predetermined positionand the hole(s) is filled with a via paste containing electricallyconductive powder and an uncured thermosetting resin is prepared, and aninner via(s) is formed upon forming the electrically insulating layer bythe heating and pressurization.
 48. The method according to claim 45,wherein as the electrically insulating substrate, an electricallyinsulating substrate wherein one or more through holes are formed in apredetermined position and the hole(s) is filled with a via pastecontaining electrically conductive powder and an uncured thermosettingresin is prepared, and an inner via(s) is formed upon forming theelectrically insulating layer by the heating and pressurization.
 49. Themethod according to claim 46, wherein the electrolytic capacitor isdisposed within the electrically insulating layer so that the inner viain the electrically insulating layer contacts with the electrode leadpart of the valve metal element for an anode of the electrolyticcapacitor.
 50. The method according to claim 47, wherein theelectrolytic capacitor is disposed within the electrically insulatinglayer so that the inner via in the electrically insulating layercontacts with the electrode lead part of the valve metal element for ananode of the electrolytic capacitor.
 51. The method according to claim48, wherein the electrolytic capacitor is disposed within theelectrically insulating layer so that the inner via in the electricallyinsulating layer contacts with the electrode lead part of the valvemetal element for an anode of the electrolytic capacitor.